"Carra made a mistake against West Ham, it's obvious, but it's the team that has to improve defensively, so I'm not worried about this," said Benitez.
"I have been talking with Carra about his physical condition because everyone has been asking about his fitness levels.
"But his fitness tests are better than the beginning of the season, so it's okay.
"Jamie is a player who is fit, training really well and has no injuries so he is taking care of himself. He has a lot of years to play.
"At this moment he is one of the best centre-backs that we have so he has to play because I am pleased with him.
"I can guarantee you I was checking the data and he is quicker than he was in August when we were doing the tests.
"During the summer you don't train for pace but stamina so in August you improve your stamina and strength. The competition means you improve your match fitness so he is quicker now than he was before. He is not going down, he is going up.
"If you are slow you are slow, but Carra is quicker now because his game intelligence is better."