Warnock's side lost 2-1 at his former club Queens Park Rangers, to leave them 15 points adrift of the play-offs.
"If we can't win here when we've dominated like that, we're not going to get into the play-offs," Warnock said.
"To get where we are has been fabulous. The lads have really done well for me."
Cardiff had led through Sol Bamba's first half header at Loftus Road before Yeni Ngbakoto equalised five minutes after coming on as a second-half substitute.
Ngbakoto's corner with seven minutes remaining was met by Matt Smith, with the ball going in off Cardiff defender Jazz Richards to end their four match unbeaten run.
The Bluebirds were in the Championship relegation places when Warnock took over in October 2016 but are now 12th in the table and 12 points clear of the drop zone.
Having recently signed a new one-year contract extension, Warnock says he considering which players to retain and which areas he needs to recruit.
"I thought today made up my mind on the odd position what I'm looking for." Warnock said after losing to QPR.
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"We've got 11 games left to look at the others to make sure.
"I'm looking all the time to see what we need to have a good go next year. We don't want to mess about next year.
"We want to start well at the start of the season and look forward to coming to places like this."
Warnock said "three or four" suffered knocks before Tuesday's trip to struggling Blackburn Rovers.
Midfielder Aron Gunnarsson played against QPR despite not taking part in training during the week due to illness.
"We're a little but short in certain areas," Warnock added.
"But I'm looking forward to Blackburn. They won again [on Saturday, against Wigan] so it will be nice to go up and try and get the points."
Cardiff City manager Neil Warnock has said he is already planning for the next campaign after ruling out this season's Championship play-offs.