The pair exchanged views before training on Monday after Benitez left the defender out of their defeat at Manchester City.
"I can understand the frustration of Terry, an important player who is trying to help and push because he wants to win," said Benitez. "But he has had problems with his knee.
"Sometimes he hasn't been able to finish the sessions because of the intensity but he's getting fitter with every session. We see after every game how he feels. Still, he has to keep training and doing those sessions and he can do better."