United currently sit atop of the Premier League table having got off to a flying start to the season, including an 8-2 demolishing of Arsenal.
Despite the brilliant form former United captain Keane believes there is more to come from Sir Alex’s men.
Speaking to Radio 5 Live the 40 year old warned,
“United to me are just going to get stronger and they are the team to beat as usual.
“And they settle straight into the team because they’ve got good habits, good attitudes and a good spirit.
“The only major question mark would be if Wayne Rooney picks up an injury, because he’s a big, big player for them.
“He is scoring goals for fun. Since he signed his contract, he has settled down and his best years are still ahead of him.”