"It's fair to say that Chelsea have an uphill fight to overcome us. But you can never be dead sure," the United boss said after the 3-0 win against Fulham on Wednesday night.
"Things can happen. You'll remember we were 12 points ahead of Arsenal back in 1997-98 and then we lost the league.
"We had a lot of injuries that season, though. Hopefully with the squad we've got now, we can cope with injuries like we've done in the last few weeks.
"That's been a development at this football club. We've got such a big squad, we can make changes.
"I was pleased for Wayne Rooney, it was a nice goal. He came in late, which I've seen him do many times, and scored with his first touch. So he's back and hopefully he stays back.
"He's 100 per cent. We're at the stage of the season where we won't take chances. If they've got slight injuries, they won't play. If they do, it could exacerbate the problem."