One of MMA's iron men has been forced to the sidelines with an injury.

Josh Koscheck, the veteran welterweight who is always among the first to volunteer for available card slots, is out of his scheduled UFC 151 co-main event matchup with Jake Ellenberger due to a bulging disc in his back.

The news was first reported on Tuesday's edition of UFC Tonight.

Koscheck had already fought twice in 2012, taking a decision over Mike Pierce while losing a split-decision to surging Johny Hendricks in the more recent bout.

He has fought 21 times during his seven-year UFC career, with notable wins over Matt Hughes, Paul Daley and Chris Lytle.

His only other extended time off came after challenging Georges St-Pierre for the welterweight title, caused by a broken orbital bone sustained during the unanimous decision loss.

Koscheck is 17-6 overall.

According to UFC Tonight, as of yet there is no replacement for Ellenberger (27-6), who was hoping to rebound from his first loss in his last seven fights.