In addition to Varney, who was dismissed for an elbow at Millwall, the Leeds boss has been denied the services of Jason Pearce and Michael Brown in recent weeks with the pair serving three and one-match suspensions respectively.
Warnock has benched both Brown and Pearce since their returns and Varney could be in for similar treatment, with the Elland Road boss warning his players he expects better.
"We've got to try and keep our discipline a little bit better," he told the Yorkshire Post.
"The two sendings off - whilst I don't think they were malicious, we shouldn't be giving referees decisions to make on silly things like that. Pearce was on the halfway line and Varney was on the halfway line. We ended up losing games where we could have got a result.
"The players concerned with the sendings off should set a lesson to all of my players. If you're going to be stupid and put yourself at risk of losing your place, you might not get it back. Brown's the same.
"A stupid booking gets him a one-match ban and he can't get back in. I hope that continues."