"We had a lot of offers from clubs who wanted to buy him in the summer - three or four clubs were interested - but we stuck to our guns because we believe in him," he told this week's Inside United magazine.
"He'll be a future centre-half for Manchester United, there's no doubt about that. That's a vindication of our belief in the boy, and also to prove to himself that he can believe what we're saying to him, that he will play a lot of football at this club. He'll get plenty of games here."
The manager also claimed the loan system had benefited him. "He had six months at Antwerp as a young kid at 17, then he had two spells at Sunderland and did really well. In fact, I think Sunderland could have been relegated last season if it wasn't for the stability of Jonny Evans.
"I watched him for Northern Ireland against the Czech Republic recently and he was very good indeed. He's only 20 years old but he's already got 11 international caps. He'll be a fixture for Northern Ireland now, I imaging he'll be their captain in time, he's an outstanding candidate for that and he's a boy with great talent. We're pleased with his progress."
The manager also claimed he had no doubts Ronaldo would receive a fantastic reception despite summer speculation of a move.
"The fans know that he's been here for five years, he's shown his loyalty to the club - he's hardly missed a game in all that time - and he's scored all these goals. He's entertained us to incredible levels and the fans don't forget these kind of things. They supported him after the World Cup thing with Wayne Rooney and I knew they would support him again this time."
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