Keane has joined Villa until the end of February and, subject to international clearance, is in contention to make his debut in Saturday's home clash with Everton.
But he had already arranged a spell training with Tottenham before making the temporary move to the midlands and has no doubt Harry Redknapp's side can challenge the two Manchester clubs for the title.
He said: "Tottenham are genuine contenders. Definitely. If you look at their form over the last 10-12 games they are on a really good run and they haven't lost many.
"They are playing some great stuff, and had another great result last night [against Everton on Wednesday].
"Harry (Redknapp) has built up a good squad there, a really strong squad.
"If you look at the squad there compared to United and City, they are certainly up there with the strength in depth they have."
Keane is relishing being reunited with another former Spurs player in Darren Bent.
He said: "Darren is a top player and has proven that over the years. Even at Tottenham, when he did play he would always score goals.
"He has proven that at every club he has been at. It will be great to play with him again.
"But there are other good strikers at Villa like Gabby (Agbonlahor) and I look forward to playing with all of them."
Keane admits his love for football persuaded him to temporarily link up with Villa and cut short his break before reporting back for pre-season training with the Galaxy.
It is a club he has been linked with many times during the past decade, since the collapse at the 11th hour of a move from Wolves to Villa in 1999 which resulted in him joining Coventry.
He said: "Initially I was going to take the break and could have been lying on a beach now.
"But I was back training with Tottenham next week. I was getting myself prepared for the MLS season anyway.
"I've had my rest of three to four weeks at the end of the season. I'm not a player who likes to sit around for eight weeks.
"I get itchy feet, and the move to Villa is good. It works out well for both of us."
Keane is hoping he can make the same impact at Aston Villa as Thierry Henry on his return to Arsenal.
Henry marked his return to the Gunners by netting the winner against Leeds in the midweek FA Cup tie at the Emirates Stadium.
Keane said: "Can I do a Thierry Henry? I hope so. It would be great to do that.
"It was written that he was always going to come back and score on his return to Arsenal.
"Good luck to him, he is obviously a legend at Arsenal.
"If I can do something like that in the six (league) games, and help the team, that is great."