Gareth Southgate has claimed that England's players are lacking "psychological freshness" following their World Cup exploits due to the Premier League season beginning too early.
Following the Three Lions' fourth-placed finish at Russia 2018, key members of the team have suffered injuries during the early stages of the new season.
Captain Harry Kane, meanwhile, has regularly dismissed suggestions that he is in need of a rest.
When asked about tiredness ahead of England's Nations League match against Spain in Seville on Monday, Southgate told Sky Sports: "I think it's psychological freshness, rather than physical.
"Everyone adapts their training load appropriately. But I think when you see the league, there are probably a lot of teams that haven't started yet at the level when they are at their maximum.
"There have been lots of injuries across our league, I don't know about the rest of Europe. It is a balance.
"I don't really understand why our league started so early, but they did, so it is a really difficult situation for the clubs."