A goal in each half by Thomas and Paul Green nudged the hosts closer to an npower Championship play-off place, while the Tractor Boys saw their three-match winning run splutter to a halt.
Mick McCarthy's men failed to trouble Paddy Kenny until the closing stages, when the veteran Leeds goalkeeper made instinctive saves from Lee Martin and substitute Michael Chopra.
Warnock said: "I am still trying to get Jerome fit enough to play a full 90 minutes. We have to treat him with kid gloves.
"It is more important to me that he plays against Middlesbrough next Saturday than Chelsea on Wednesday, so we will have to see. Knowing Jerome, he will want to play against Chelsea.
"I won't play my full team and I am sure Chelsea won't, but they have more players they can rest than we have. I am sure it will be competitive, whatever team I put out."