After finishing in their lowest-ever Premier League position of seventh last season, the Red Devils spent around £150m this summer, but the legendary former full-back thinks that they still aren't strong enough at the back.
He told Sky Sports News: "I don't think they can [win the league], no. Chelsea and Manchester City are the two strongest teams.
"I think when they come up against the big sides, defensively, they will have problems dealing with them. What they are [after their signings] is closer to the title than they were three weeks ago.
"With respect to the season after, you can see some light at the end of the tunnel with the players they have signed."
United beat Queens Park Rangers 4-0 on Sunday.