“I don’t think the discussions we’re having now are anything new,” he said on Sky Sports’ Monday Night Football.
“We said at the start of the season that Manchester United needed a centre-back, and that there were question marks over the goalkeeper.
“The key thing is that only one of the last 20 Premier League champions have conceded at least one goal per game,” he added.
“That tells you about these three of De Gea, Lindelof and Maguire. To win titles, that triangle of goalkeeper and two centre-backs need to be as solid as a rock.
“They concede too many goals and if you concede one or more goals per game, you’re not going to win a Premier League. Manchester United have to look at that.”