Former England coach Sir Clive Woodward says the British and Irish Lions tour of New Zealand last year is the reason behind England's poor showing in the Six Nations.
16 England players made up the 41-man Lions squad which played 10 matches in New Zealand last year, including an impressive drawn series against the World Champions.
England finished fifth in the Six Nations followed a 24-15 defeat to grand slam winners Ireland on Sunday, the side's third straight loss.
Woodward, who coached England to the World Cup title in 2003, said the main reasons for England's fatigue was Lions tour.
"Why has it happened? I wouldn't overstate what happened on the Lions tour," he told BBC 5 live.
"As a fan I love the Lions, as a coach I didn't like it one bit. The way the Lions players are set up and play so many games with their clubs it's a bad year.
"Maro Itoje looked out on his feet and wasn't the same player we saw last summer against New Zealand. It's taken its toll on them."
11 Irish players were part of the Lions tour along with 12 Welsh and two Scottish players.
Woodward's comments echo that of former England centre Jeremy Guscott said a long Lions tour along with club and country commitments is mentally draining.
"Mentally, going on a Lions tour and then coming back to a long domestic and international season makes a huge difference. The Lions is so big, I can't explain how mentally draining it is," Guscott wrote for the BBC.
"These days the players are constantly monitored by their club and country with the most advanced sports science methods, so the coaches should be able to tell if they're drained, and they shouldn't be picking them if that's the case.
"No player is ever going to say they're mentally drained, but as a player you don't realise it and that's where the management have to step in."