The 29-year-old was due to start Saturday's Premier League clash against Blackburn but picked up a suspected broken metatarsal during a training session Thursday.
Warnock revealed the injury will keep Campbell out for at least four weeks, but could leave him on the sidelines for up to two months should the bone require pinning.
"He had an accident on Thursday in the last kick of the training game," Warnock said after watching QPR draw 1-1 with Blackburn.
"It looks he has got a metatarsal problem so he could be out for a few weeks.
"I think it will probably be longer than four weeks and he might have to have an operation. We'll know Monday.
"I think it is these stupid boots, they're like carpet slippers.
"Don't talk to me about these boots.
"You can't ban people if they prefer it, but I think they are absolutely stupid boots to wear at the level we're talking about.
"They give you no support at all, but that's football."
With Campbell ruled out, QPR striker Heidar Helguson got his first start of the season.
The 34-year-old did not disappoint at Loftus Road, giving the west Londoners a 16th-minute lead thanks to a deft cross-shot.
Christopher Samba equalised eight minutes later with a towering header after latching on to Jason Lowe's corner, meaning the sides left with a point apiece.
"I can't fault the lads," Warnock said. "I thought they tried hard today.
"Coming on from that [6-0] defeat [to Fulham] in the last game, it was good.
"The main thing I am so disappointed with was the goal that we conceded.
"You have to make teams earn the right to score a goal and if you can't mark a man at a corner for a free header then there is something wrong.
"I am really disappointed about that."
On Helguson's goal, Warnock added: "He meant to do it. He was unlucky with his header and how they got that header out I'll never know.
"I thought he played ever so well today and I would probably give him my man of the match if I had a choice."
While Helguson's starting role surprised many at Loftus Road, visitors of a QPR web forum were already aware of the news.
Campbell's injury and the squad changes were leaked by a forum member, who received the full force of Warnock's wrath in the post-match press conference.
"We have got a website where a QPR fan puts on [information] on the website yesterday after we'd had the accident," he said. "I can't believe it.
"[Name removed] puts on this website that Campbell has broken his foot, Helguson is playing and Mackie is making his debut, while Adel [Taarabt] is out.
"This is supposed to be a supporter. You don't want many supporters like that.
"What an advantage for the opposition. You don't gain anything from that. Obviously he has got a contact, hasn't he?
"But if he thinks he is helping me, if he is a QPR fan, it is exactly the opposite.
"I don't understand supporters like that unless it is to get a bit of kudos with his mates.
"It does my head in things like that."
Blackburn manager Steve Kean was obviously unaware of the leak as he admitted to deploying Jason Lowe in a defensive midfield role to mark talisman Taarabt.
The Rovers boss has come under increasing pressure recently and was frustrated not to leave Shepherd's Bush with three points.
"I suppose any point away from home is a good point," said Kean. "That said, we were slightly disappointed.
"We felt the first goal was against the run of play but fair play to QPR.
"They mixed up their set plays and we ended up changing our markers at the corner to our detriment because I know Helguson very well.
"He lost his marker at the first header and then fair play to him, it is a top finish.
"But we were slightly disappointed as we felt we were on top at that point.
"Having said that, we never felt sorry for ourselves.
"We grabbed the game by the scruff of the neck and showed a good reaction to going behind."