Credit: FameFlynet

Brad Pitt can't always lean on Angelina Jolie when he's in pain -- which might explain why he's using a cane!

The 48-year-old actor stepped out in Beverly Hills Thursday with the aid of a walking stick. "He tore his MCL," a source tells Just Jared, explaining that Pitt injured one of four ligaments that stabilizes the knee joint.

The cause of the World War Z actor's injury is not yet known -- nor is the reason he chose to wear an all black jumpsuit.

As of now, Pitt is still expected to walk the red carpet at the 69th Annual Golden Globes on January 15. The Tree of Life actor is nominated for Best Actor in a Motion Picture Drama alongside George Clooney (The Descendants), Leonardo DiCaprio (J. Edgar), Michael Fassbender (Shame) and Ryan Gosling (The Ides of March).