Problem: Article: The 21-year-old made 13 appearances in all competitions for the Exiles while on loan at the Rodney Parade club earlier this season, scoring one goal.
He previously spent three months with Port Vale in 2015, playing five games for the League One side.
O'Sullivan is yet to start a Bluebirds first-team match, but has made three substitute appearances for Cardiff.
Find all the latest football transfers on our dedicated page.
Answer: [[Newport County have re-signed Cardiff City midfielder Tommy O'Sullivan on loan until the end of the season.]]

Problem: Article: Ex-enterprise minister Jonathan Bell told the BBC that top advisers from his DUP party stopped him from restricting the Renewable Heat Initiative.
The BBC said an interview with First Minister Arlene Foster, who is facing calls to step aside while claims are probed, was a "contrasting account".
"This is a matter of high public interest," the corporation added.
The interviews, conducted by the BBC's Stephen Nolan and broadcast on Thursday, contained a series of claims and counter claims.
Mrs Foster has apologised for not putting a cap on the costs of the lucrative scheme but denies any intervention that may have prolonged it. It is estimated the way the scheme was set-up will cost taxpayers Â£400m over its 20-year lifetime.
In a statement on Friday morning, the DUP said Mr Bell's allegations were a "tactic to distract from fact he as minister made the crucial and catastrophic decision to delay RHI cost savings in autumn/winter of 2015."
"It is a matter of regret that BBC has fallen for his spin," the party added.
"The BBC broadcast claims from a former minister about documents in relation to the RHI controversy as well as a contrasting account from the first minister," a spokesman said.
"All those referred to in the broadcast were afforded rights of reply, which were aired. This is a matter of high public interest and the BBC believes it was entirely proper to bring this to our audience."
Answer: [[The Democratic Unionist Party has accused the BBC of falling for "spin" over a flawed green energy scheme.]]

Problem: Article: Militants linked to so-called Islamic State have been occupying parts of Marawi, a city in the south, since May.
President Rodrigo Duterte said the extension was necessary to crush the insurgency, but his critics say it is part of a wider power grab.
Mindanao is home to a number of Muslim rebel groups seeking more autonomy.
Martial law allows the use of the military to enforce law and the detention of people without charge for long periods.
It is a sensitive issue in the Philippines, where martial law was imposed by the late dictator Ferdinand Marcos for much of his rule.
A previously imposed 60-day martial rule was due to expire on Saturday. It went into effect on 23 May, just hours after deadly clashes between the army and gunmen linked to so-called Islamic State.
The extension means the law will now remain in force until 31 December.
In May, President Duterte warned that martial law could be extended across the Philippines after insurgents killed police officers in Marawi.
Some opposition lawmakers questioned why it should be applied to the whole of the southern island, instead of just the city.
"I fear that the plan to extend the martial law in Mindanao will pave the way for a Philippines-wide martial law," Senator Risa Hontiveros was quoted by AFP as saying.
Another senator, Franklin Drilon, said the extension was too long, while congressman Edcel Lagman said there was "no factual basis" for it.
A dozen protesters also interrupted proceedings at Saturday's hearing, chanting "never again to martial law", the news agency reports.
Army chief of staff General Eduardo Ano said it was necessary to restrict the movement of the Islamist militants, warning that the ongoing rebellion could spread to other cities on the island, the GMA News website reports.
He described it as a "Mosul-type, hybrid urban warfare", referring to fighting in the Iraqi city that was until recently held by IS.
Security officials addressing congress ahead of the vote said the law was required to stabilise the region, where supporters of IS may be inspired to stage similar uprisings in other areas of Mindanao.
They said only about 60 gunmen were left in a 49-hectare area of Marawi, but nearly 1,000 pro-IS militants were active elsewhere in the south, holding 23 hostages.
Marawi was home to 200,000 residents but many have fled the violence. There are fears for those trapped who face a lack of food and water.
More than 420 militants, 100 soldiers and 45 civilians have been killed in the fighting.
Clashes began when the army failed in its attempt to capture Isnilon Hapilon, believed to be the main IS leader in the Philippines and linked to the local Maute group, which has declared allegiance to IS.
In response the Maute group attacked parts of the city, taking hostages.
Answer: [[Legislators in the Philippines have voted overwhelmingly to extend martial law to deal with an Islamist insurgency in the restive island of Mindanao.]]

Problem: Article: The Team BMW driver from Portadown finished second in the wet race three, coming home behind Honda's Shedden.
Turkington was later awarded the victory, the first for Team BMW, ahead of Adam Morgan and Ash Sutton.
Aiden Moffat, who collected his maiden win, and Tom Ingram were the other race winners in an eventful day.
Turkington had a strong start to the weekend, working his way up to fourth after starting in 10th place.
Yellow flags at the final chicane meant he couldn't pass Rob Austin despite being the quicker driver in the latter stages of the race.
In race two, Turkington struggled on the soft tyre in the opening stages of the race before going on a charge at the end, overtaking reigning champion Shedden with two laps to go to claim fifth.
Turkington completed a solid weekend in race three, coming home behind Shedden after overtaking pole sitter Dave Newsham on lap nine.
The race was initially red flagged after several cars aquaplaned off the circuit, and the race was reset after a brief wait for the conditions to clear up.
Turkington leaves Donington Park second in the standings, 15 points behind Ingram.
It was another luckless weekend for Carrickfergus driver Chris Smiley, whose strong pace didn't yield the results it deserved.
Starting 20th, Smiley worked his way up to 16th before being punted off by Tom Chilton, taking both drivers out of the race.
After his first race incident, Smiley started race two from 26th, dropping down to 29th by mid-race.
A sensational final five laps moved the 25-year-old up the order, crossing the line in 17th place and his best result of the season.
Smiley made the most of the torrid weather conditions in race three, moving his way up to seventh place before the red flag reset the order.
The BTC Norlin driver was forced to start from the pit lane at the restart, coming in 18th but moved up to 17th following Shedden's disqualification.
In the support races, Northern Ireland racers had a successful weekend at the East Midlands circuit.
Belfast's Charlie Eastwood dominated in the Porsche Carrera Cup, taking pole position for both races as well as collecting both wins as he continued his strong start to the championship.
Eastwood has now taken the lead in the championship, four points ahead of team-mate Daniel Cammish.
Hillsborough teenager Dan Harper had a strong weekend in the Ginetta Junior series, taking victory in the second race.
Another podium and a sixth-placed finish means that Harper leaves Donington second in the championship table, five points behind Tom Gamble.
At the first round of the European Le Mans Series at Silverstone, Templepatrick driver Wayne Boyd claimed a podium for United Autosports.
Answer:
[[Colin Turkington was moved up from second to first place at Donington Park after Gordon Shedden was disqualified for failing a ride height test.]]