Breaking News: John McEnroe gives Novak Djokovic retirement verdict with ‘fear factor’ message…see more

“How long can this guy keep motivated? Then he won the Olympic gold. I’m amazed that he’s kept it (motivation) for this long.”

“I’m sure to be surprised either way,” the American added. “If he doesn’t win (a major), you would be like wow – he won three of the four last year. And now we’re saying he’ll never win it again.

“And then I would sort of be surprised in a way if he did, because (of) his age. At some point, that catches up to you, and you lose a little bit of that fear factor with some of the guys.

“Then guys that didn’t think they had a chance feel like they have a chance, and that whole thing changes and makes it much tougher.

That’s what he’s facing right now. It will be interesting to see if he’s able to pull it off. But I do think he’ll try to find that motivation to get number 25.”