Former Manchester United captain Rio Ferdinand said he had spoken to Ronaldo this week after reading reports linking him with a move to rivals Manchester City.
He also said Ronaldo had spoken to former manager Sir Alex Ferguson before agreeing a return to Old Trafford.
“Sir Alex played a massive part,” Ferdinand said. “There was no way Cristiano was coming to Manchester United without speaking to Sir Alex. Simple as that.
“The attention on the club, the attention on the other players – you can’t put into words what it’s going to do for the dressing room and the fan base,” Ferdinand added.
“He’ll get you 25-30 goals this season. That’s what he does – he outscored Romelu Lukaku last year in Serie A, but what he can do for Mason Greenwood, Marcus Rashford and Jadon Sancho alone is worth bringing.
“He will show them what an A-lister, genuine superstar and an absolute obsessive professional lives and breathes on a daily basis.”
Speaking on BBC Radio 5 Live, Michael Owen added: “Manchester United need a centre-forward who can bang in 25-plus goals a season; they haven’t had that for a while.
“He’s not a signing to appease the fans, he will be playing in all the big games. He definitely has a year or two more in him where he can score more than 20 goals.
“If he could score 30 goals this season I would be lost for words, but I wouldn’t put anything past him, even now.”
Owen Hargreaves, who won the Champions League alongside Ronaldo in 2008, said: “I remember my first day training with him. He was the first person on the training pitch, the first person in the ice bath and then the first person in the gym.
“I remember him doing sit-ups and at the end of his set he sat up and said: ‘I’m going to be the best player in the world at the end of this year.’ And he was.
“His dedication to his craft is equal to his talent, which is remarkable.
“Everyone thinks it’s all about him, but he wants to win. He’s coming back to United to win and that’s why I think as a mentor for these young guys at United he is the perfect fit and I think it’s going to be fabulous to watch it all.”