Chelsea boss Thomas Tuchel admits Saul Niguez struggled in their 3-0 win against Aston Villa.
Romelu Lukaku struck twice, with Mateo Kovacic also scoring for the hosts.
Tuchel said, "I had the feeling that he struggled.
"There were some big mistakes, passing mistakes, and he struggled with the intensity. You could see he isn't fully adapted. It's completely my responsibility. I had the feeling he could jump in for us and play at that level.
"I thought it was maybe better to change him, but it doesn't change anything."
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