Kiefer Sutherland. (AP File)

Prison Break star Robert Knepper has credited Kiefer Sutherland with saving his acting career - by punching him.

Knepper, who played villain T-Bag in the hit TV drama, contemplated quitting acting after struggling to land any roles.

But 24 star Sutherland was determined not to let Knepper give up, and literally knocked him back to his senses with a heavy blow.

Knepper recalls, "Ten or 15 years ago, Kiefer used to go to the same gym as me. I remember telling him that I wanted to quit (acting). It was before Prison Break and I couldn't find any work and I wanted to quit.

"He f**king punched me! He punched me so hard. He told me, 'Don't you ever give up!' and I thank Kiefer every day for that advice."