9:21 AM -- Ryan just tweeted the injury is the result of a freak accident, NOT an injury he suffered doing a stunt or anywhere near the set of "Shooter."

Ryan Phillippe's learning the hard way ... breaking a leg as an actor ain't always a good thing.

The "Shooter" star is laid up in a hospital bed with his right leg bandaged up -- also looks like he has a cast around his ankle. It's unclear what he broke, but based on the hardware fixed on the leg ... we're guessing there was some surgery involved.

No word if it's a work related injury, but Ryan captioned the pic, "I'm going to be ok and I appreciate your concern." A few hours later he changed his tune a bit, tweeting, "this sucks."