Shaw impressed many with his performance in the Champions League win over CSKA Moscow.
But Scholes, who has done some coaching work at Carrington, revealed: "It's difficult to say as we don't see what goes on behind the scenes. I don't think he lives his life as clean as he possibly should do.
"With his body shape, he looks like a player who needs to be playing every week. We had Wayne Rooney, who was a player if he missed a couple of games you knew, he wasn't looking after himself.
"He needed to be playing all the time, Saturday, Tuesday, whatever it may be.
"I hope there is a future for him. A couple of years ago, I thought we were signing the best left back in the world."