Biggest Loser Contestant In Critical Condition

It's unclear how he fell -- but sources close to Sam Poueu tell us ... he suffered a pelvic injury, torn ligaments, a punctured lung, and a broken leg during the accident.

According to sources, Sam -- who was a fan favorite on the show last year -- is currently recovering in the ICU -- but while he's listed in critical condition, we're told he can still recognize visitors.