The Scottish international is facing at least a month on the sidelines after badly twisting his ankle in Saturday’s defeat at Cardiff City.
With fourth-placed Hull City due to visit Elland Road tonight and Nottingham Forest, who sit sixth in the embryonic table, at the weekend, United’s striking resources will be tested to the limit with Warnock admitting that the chances of getting a loanee in are slim.
The Leeds manager said: “Ross is going to be out for a while and that is a big, big blow for us.
“We could probably get away without anyone but him, especially after the start to the season he has had.
“He is a major, major player for us. I want to bring someone in on loan but most of them have gone.
“Unless something unexpected comes along, I can’t see us having anyone in before the Hull game so we have to go with what we have got.”
McCormack’s ankle injury, sustained in the first three minutes at Cardiff, means United have lost three of their first-choice XI in quick succession with midfielders, David Norris and Paul Green, being ruled out ahead of the international break.
It means the club’s squad is already being stretched to the limit, just as Warnock had warned could happen before a ball was kicked.
Adam Drury is also a doubt tonight to add to the manager’s headache with a muscle strain as United prepare to take on a Hull oufit fresh from thrashing Millwall 4-1 at the weekend.
Warnock said: “Hull are flying at the minute and will be really looking forward to coming to Elland Road.
“But we have done well at home. The crowd will be important because losing Ross is a blow so we need the fans to get right behind us.
“All I can ask is for the lads to give everything and the fans to do the same. As I said, we have done well at home so, on paper, two home games in a row gives us a good chance to push on.
“It won’t be easy, though, as both teams are doing well. I expect them both to be up there all season. Hull spent quite a bit in the summer, particularly on the lad up front (£2.6m summer arrival Nick Proschwitz), and Steve is a good manager so they will be a tough opponent.”