The FIFA World Player of the Year lifted the trophy with the Red Devils in 2008 and lost to Barcelona in last season's final in Rome before completing a world record £80 million move to Real Madrid.
The 24-year-old opened his Champions League account with his new side on Tuesday night, scoring two free-kicks as the Madridistas walloped group whipping boys FC Zurich 5-2 in Switzerland.
However, former Barcelona forward and Match of the Day host Lineker believes Real's latest collection of superstars, including Kaka, Xabi Alonso and Karim Benzema, will struggle to keep clean sheets, and that Ronaldo would have better placed to triumph in Europe again with Sir Alex Ferguson's side.
"I had no problem with Cristiano Ronaldo joining Real Madrid this summer. Players want to move clubs for lots of different reasons. Sometimes they just fancy a fresh challenge," he said in the Mail.
"I understand that, I did it myself. But for this season at least, I think Ronaldo would have had a better chance of winning the Champions League if he had stayed at Old Trafford.
"Real defend awfully and the top sides in Europe will fancy their chances, even though Ronaldo threatens danger at the other end.
"I still make Barcelona favourites. Their forward line of Messi, Ibrahimovic and Henry, backed up by Iniesta and Xavi, is as good as Real Madrid's and their defence is better.
"It is going to be fascinating and exciting to see if Ronaldo and Real Madrid can prove me wrong."
