Clarke says Reid, 31, is ruled out of tomorrow's derby against Aston Villa after seeing an old leg injury flare up after training.
But the Albion boss explained: "Steven picked up a fractured fibula - he played for 45 minutes with that broken leg at Arsenal. He's come back and picked up another knock in the area.
"It's not serious but he won't play against Villa. We are trying to protect him from himself. I want to tell people about his strength of character. People always think he is injured. But he wants to play."