Manchester United defender suffered a knee injury last week.
Defoe said: "Credit to Rio, he could have gone home and gone on holiday.
"But he chose to stay here and be with the players and, even though he is on the sidelines, he is the captain and credit to him.
"When he got injured, we couldn't believe it. It was a freak accident in training.
"It happens but we are all here for him and he is a fantastic guy."