Manchester United icon Andy Cole has warned his former club not to get carried away by their excellent start to the new season, warning it remains a long way behind Real Madrid ahead of the Champions League.

Cole, who managed a United legends team in a 2-2 draw against Barcelona at Old Trafford on Saturday, has been impressed by Jose Mourinho's side winning all three of its opening Premier League matches without conceding a goal.

But he feels the UEFA Super Cup defeat to Real Madrid should not be forgotten in a hurry, and believes European glory this season is a tough ask, ahead of United's return to the continent's elite club competition at home to Basel on September 12.

"It's massive for the club [to be back in the Champions League], because that gives you another platform to bring in the players that you need," Cole, who won the tournament in 1999, told reporters.

"That is what the fans want and what they expect at a club like Manchester United. So that is major as well. 

"It gets tougher and tougher to win that Champions League. If you look at the team that has won it two years on the bounce now, we played them in the Super Cup and I think you saw the gap there. 

"There was a big gap between Real Madrid and Manchester United. And Real Madrid had some of their better players on the bench as well. 

"So to win that competition you are going to have to be in tip-top condition."

Cole is also cautious about proclaiming United as Premier League favourite given the competitive nature of this season's title race, despite his delight at its strong start.

"There's a long way to go, it's a marathon not a sprint," he said. 

"You can't say they are favourites for the title because they bought some good players. They finished sixth last season, yes they have brought in some really quality players, but the Premier League this season, there are six teams that could win it. 

"United will be up there but I don't think anybody in this moment in time could put a marker down because it is so up and down this league. 

"It's a great return, 10 goals, none conceded, creating chances, scoring goals, looks like we're playing half decent football. So yeah, I'm more than happy.

"Manchester City started as favourites and I don't think people were really talking about Manchester United, but after the start people are saying [maybe], but it is a long, long way to go."