Ahmed Sabra, a UK citizen who holds a British passport, was visiting family in Gaza with his wife and three children at the start of the war.
His wife and children were allowed to cross into Egypt on Thursday, butDr Sabra was turned away.
The Foreign Office said it was working to get all British nationals home.
Dr Sabra, a consultant cardiologist at Pinderfields Hospital in Wakefield, West Yorkshire who was a cardiology registrar at Morriston Hospital, Swansea, said he had made it through the Rafah crossing on Monday and was waiting to get his passport stamped.
Former colleague and friend Sara Gretton, who worked with him in Swansea, toldBBC Radio Wales Breakfastthat he had messaged her overnight to say his name was now on the list of British nationals eligible for evacuation and he was heading to the border.
Thousands of foreign nationals have been making the same trip to the only open crossing out of Gaza, but only those named on a list, published daily by the Gaza Border Authority, are allowed to cross.
Those on the list must be cleared by both Egyptian and Israeli authorities.
Ms Gretton and Dr Sabra's supporters asked why he was not on the list last week.
"It seems so simple you know - the Foreign Office informs the agencies that he is a British national, his name should be added to the list, it should be published and he should be evacuated."
"I just don't know what has gone wrong since last Thursday, and that hasn't been done."
Hamas's attacks on Israel on 7 October sparked the war. Hamas gunmen killed about 1,200 people and took 240 others hostage in its unprecedented cross-border assault it launched that day.
After a month of Israeli bombardment and nearly two weeks after Israel launched a major ground offensive into the territory, Gaza's Hamas-run health ministry said on Friday that 11,078 people had been killed, while 1.5 million had fled their homes.
Dr Sabra's former colleagues at Morriston Hospital held a rally on Monday in support of his safe return home.
The Foreign Office said it was working "round the clock to ensure all British nationals in Gaza who want to leave are able to".
A UK doctor who was stuck in war-torn Gaza when his name was left off a list of British nationals has finally reached Egypt.