Yorke has retired after leaving Sunderland at the end of last season.
But he told the Independent: "I'm as fit as I can be, and if I played with United tomorrow I'd easily fit in, because I'd have such good players around me. Lesser teams have to do a lot more running, so with a lesser team I might get caught out. But United keep the ball, and make the right pass at the right time.
"That's why Ryan Giggs is still doing so well. And he's kept up with all the changes. I was there [at United's Carrington training ground] just a few days ago and there have been so many changes. We also had a swimming pool but now they have a treadmill in the swimming pool. They have different kinds of massage. Yoga. These are the things Giggsy is doing."