Chelsea and Arsenal sit two points behind United, but Carlo Ancelotti's side have a game in hand on the reigning champions.
"We are back in the lead, but Chelsea have a game in hand," Ferguson said.
"It's also going to be a hard-fought tussle, with Arsenal coming strongly now, and I have a suspicion that they might yet mount the biggest challenge."
However, Ferguson was careful to add the most important caveat when discussing Arsenal.
"To a certain extent the title is in our hands because Chelsea have to come to Old Trafford (on April 3) and naturally that will be a massive match, but, as I say, I'm wary of Arsenal if they don't suffer too many more injuries to key players."
Ferguson also believes that this could be the tightest title race in years.
"Right now it's looking like it, I must say. It's looking very tight. We have only got eight games left, Chelsea have nine games left, so you never know. You have to think about goal difference. We're four goals ahead of Chelsea. I wish it was 14, but at least it's something in our favour.
"I suppose the simple way for us and Chelsea to look at it is just to win all our games. But life is never that simple."
Barclays Prem 2009/10 Win Outright: Arsenal 9/4