Big Norman, who made his United debut at the age of 16, told The Sun: "I remember one of my old youth coaches saying you can't call yourself a good pro until you've got 300 or 400 games under your belt.
"Once you reach that kind of total, people look up to you because you've shown you can perform consistently at the highest level.
"When you talk of world-class players you've got to look at guys who have won the World Cup and the biggest trophies around.
"It's a massive title and you really do have to earn it.
"I think it's the same with Wayne Rooney.
"Both he and Ronaldo have got great potential but there's some way to go before you can say they're the best."