The Los Angeles Galaxy midfielder can see the Eastlands club challenging at the top of the Premier League in the coming seasons but suggested that there is still a gulf between them and his former club.
"They may have great players in the team, but they are never going to be Man United," he told Sky Sports News. "I've always said that.
"They might be a threat against teams this season and seasons to come, but Manchester United have the history and silverware over the last 20 years."
The 36-year-old won ten major honours, including six Premier League titles, during his ten-year spell at Old Trafford.