Huddersfield midfielder Neil Danns volleyed home his first goal for the club in the 54th minute and although Leeds substitute Aidy White headed home with his first touch soon after, James Vaughan held his nerve to slide home an 86th-minute winner for the visitors, who triumphed 2-1.
A first home defeat for Leeds since early February following three straight draws leaves them four points adrift of the play-offs with eight games remaining and Warnock admitted the loss felt "like a fatal defeat".
"I'm obviously disappointed, but I can't fault the players, they put everything in," he said. "We've had so many opportunities now over the last six to eight weeks to be 10 or 12 points better off.
"The problem is we're always chasing the points to get back in there. It almost felt like a fatal defeat because of the points situation."
Warnock, who arrived at Leeds in February 2012 with the hope of becoming the first manager in Englaish football to win promotion eight times, said he would be prepared to step dowen as manager when his side's play-off chances are mathematically over.
"Realistically we're running out of games and (the owners) GFH know my situation, I speak to them on a regular basis," the 64-year-old said.
"Once we're out of contention for the Premier League they know I won't be having another year in the Championship.
"They've got to look after themselves really. We've spoken about my successor, about people coming in if mathematically it's impossible to get into the play-offs.
"I'd like to think that I'd have an input on that because the job we've done over the last 12 months, the staff and I, I think's fantastic."