Manchester United's hectic schedule means they must stay mentally strong if they are to remain competitive on all fronts, according to Jose Mourinho.
United sit joint-top of the fledgling table after five wins and a draw from their opening six matches, level with Manchester City at the summit.
Their return to the Champions League has also started well, with a 3-0 win over Basel followed by a comprehensive 4-1 thrashing of CSKA Moscow on Wednesday.
However, just three days later United face Crystal Palace in the league and Mourinho is not happy with the preparation time for the Old Trafford clash.
"When I looked at the fixtures, I only looked to the period of time we have to recover from match to match," he told a media conference.
"It's the only thing that concerns me. It is very important.
"We played Wednesday night and we arrived [in] Manchester [at] 4am, so [we got] home at 5am, and we have to [play] tomorrow, so [our] mentality is [always] very important."
"We have to train and make decisions after training," says the boss. "I hope some of the players that couldn't play in Moscow can recover." pic.twitter.com/safealRoFp
-- Manchester United (@ManUtd) September 29, 2017
Some may see Palace as an easy return to domestic action given they have suffered the worst start ever to a Premier League campaign.
However, despite the Eagles failing to gain a point or score a goal, Mourinho does not believe Palace should be written off yet.
"There is a long time to go," he added when asked about Palace's plight. "It is just the beginning.
"He [Roy Hodgson] is an experienced manager with good players, and they have a long time to fight and reach their objectives."