Man United officially confirmed on Friday that they had reached an agreement with Juventus to re-sign Ronaldo, a former Red Devils player.
Ole Gunnar Solskjaer’s side finished in the second position on the Premier League table last season behind champions Manchester City.
But Bent believes Man United will finish in fourth position this season behind Chelsea, Man City and Liverpool despite Ronaldo’s return to Old Trafford.
“Ronaldo looks after himself, so I don’t think there is going to be a drop-off in terms of the ultimate professional,” Bent told talkSPORT.
“He will score the goals, I still don’t make Manchester United favourites [to win the Premier League title]. I still put Liverpool ahead with Chelsea and Manchester City.
“I think Manchester United will come fourth, I still put three teams ahead of them.”
Meanwhile, Ronaldo scored 118 goals in 292 games in his first spell at Man United before he left the club in 2009 for Real Madrid.