The Sun reports how the 28-year-old forward has been heavily linked with a move away from the Santiago Bernabeu, with two years to run on his existing contract, and no signs of signing a new deal.
New Red Devils boss David Moyes has been credited with an interest in bringing Ronaldo back to Old Trafford, four years after he left Manchester United to sign for Real Madrid in a big-money £80million deal in 2009.
However, any hopes the Premier League champions might have held of re-signing the Portugal international have now been dashed, following Ancelotti's latest comments.
"I don't think there is a chance that he will leave," said the Italian. "He's our most important player and his future is here.
"We have to help him do his best because if he does that we have a great opportunity this season."
Former Real Madrid boss Jose Mourinho also dismissed Manchester United's chances of sealing Ronaldo's signature, intimating his belief that the player would not follow him back to the Premier League this summer.
"What I know is that Madrid is such a rich club they don't need to sell," he said. "It is such a rich club I think they can 'eat' any offer a club can have on Ronaldo.
"I know Ronaldo loves Manchester United and I know he loves the Premier League but I think he is going to stay. It's just a feeling, I've had no contact, nothing like that — it's just a feeling."