Clive Woodward believes the British and Irish Lions tour to New Zealand left England's stars too drained to thrive at the Six Nations.
England were dethroned as Six Nations champions by Ireland, who sealed the Grand Slam with a 24-15 win at Twickenham on Saturday.
Eddie Jones' side finished fifth in their worst tournament performance since 1987.
Significantly, a host of English players were in the Lions' squad in New Zealand last year and former England coach Woodward believes that damaged their hopes of retaining the Six Nations crown.
"You can't overstate what happened on the Lions tour," Woodward told BBC Radio Five Live on Sunday.
"As a fan I love the Lions, but as England coach I did not like it one little bit.
"Every time the Lions toured, the way our players have to play so many games for their clubs, it meant you would have a bad year and the stats tell you that.
"Certainly yesterday (Saturday), but also against France and Scotland they looked tired.
"Maro Itoje looked out on his feet and not the same player who played against New Zealand last summer.
"It's taken its toll on them. As head coach you need more control over your players."
Woodward also claimed Jones' intense training sessions would have added to England's fatigue at a time when they needed more rest.
"The off season is going to be so important for England because they need some spring back in their step because they look like a tired team," he said.
"Eddie trains them really hard and they looked very tired throughout the Championship. It's caught up with them.
"They haven't become a bad team overnight, but they haven't played well. For me a lot of it is because they look fatigued
"We haven't just been losing, we haven't even been firing any shots. They're out on their feet."
© 2018 AFP