Mark Wahlberg's boxing obsession has led to serious injuries for some of his friends.

The 39-year-old actor developed a love for the sport while training for his new movie 'The Fighter'but admitted he sometimes took it too seriously, even away from filming.

He said: "I feel bad saying it but I've fractured a lot of ribs on other people and a lot of concussions. One friend had some bleeding in the brain and that wasn't good and it happened at my house. We're still friends and he came back to train. We never punched in the head again but we'd still spar to the body."

Although he felt bad about cracking another pal's rib, Mark admitted he couldn't stop himself from laughing at his friend's misfortune.

He explained in an interview with the Independent newspaper: "Another guy cracked his rib on this side and then he tore the muscles on The Other Side in pain and he kind of collapsed holding both sides and his pants fell down to his ankles.

"We felt bad that he was hurt but it was so funny that his pants fell down.

"But those are the risks you take going into The Ring. Everybody who goes in is aware of that."

Mark - who has four kids, Ella Rae, seven, Michael, four, Brendan Joseph, two, and 10-month-old Grace Margaret with wife Rhea Durham - revealed his love of boxing has now been passed on to his sons, who often fight their superstar dad in the ring.

He said: "My kids love to go in the ring. My sons take karate, which teaches them a lot of discipline but the only one they can fight with is daddy and they like to do it every chance that they get."