Surgery is a possibility, although treatment for the injury has not been finalized, according to the team. Starters Johan Santana and Chris Young both previously tore their anterior capsules and underwent surgery as a result.
Byrdak was placed on the disabled list prior to Friday's game in San Diego after complaining of shoulder soreness. The left-hander suffered the injury after throwing a slider in Arizona on July 26.
Byrdak is 2-2 with a 4.40 ERA and leads the majors with 56 relief appearances this season. New York promoted left-hander Garrett Olson from Triple-A Buffalo to replace Byrdak on the roster.
Also on the injury front, backup catcher Rob Johnson is day to day with a bruised right hand. Johnson suffered the injury in Sunday's 7-3 loss to the Padres.
Outfielder Kirk Nieuwenhuis, currently in Triple-A Buffalo, has been diagnosed with a partial tear of the plantar fascia in his right foot and will report to Port St. Lucie for rehab. At this point, there is no plan for surgery, though that could change.
Mike Mazzeo is a frequent contributor to ESPN New York.