Bellator lightweight champion Brent Primus has been forced to withdraw from his April 13 title defense against Michael Chandler after suffering an injured knee, MMA Fighting has learned.

As a result, Chandler will now face Brandon Girtz in the main event of the Bellator 197, which is set to take place at the Family Arena in St. Charles, Mo., sources say.

Chandler (17-4) is coming off a win over Goiti Yamauchi in January, while Girtz (15-7) most recently defeated Luka Jelcic in December.

It’s unclear at this time how long Primus will be out for. The Chandler rematch would have been his first title defense after winning the 155-pound belt at Bellator NYC last June by defeating Chandler.