Avram Grant does not believe Manchester United will emulate Arsenal and make it all the way through a season without defeat. United are unbeaten so far, with seven draws and eight wins from 15 league games, and have yet to concede a goal in Europe.
Sir Alex Ferguson is set to make several changes for Tuesday night's Carling Cup quarter-final at Upton Park.
Grant went head to head with Ferguson in the 2008 Champions League final, when his Chelsea side were beaten on penalties in Moscow as United added European glory to their domestic title.
"It has happened before with Arsenal, but I don't think it will [again]," said Grant.
"What happened with Arsenal was exceptional. I don't believe there is a team which can last all the season without losing."
The former Portsmouth boss, however, is in no doubt United will be leading the chase for honours again in 2011.
"When I was at Chelsea, Alex [Ferguson] described that season as the best season ever - but even then they did not start so well," Grant said.
"You don't need to be at your best in the first few months, but at the end of the season.
"Alex is very clever. He does it every year. I can't remember one season when United started with full power."
