Zimmermann says he won't negotiate a new contract once the regular season begins, Jamal Collier of MLB.com reports.The pending free agent seemed destined to hit the open market after the 2015 season once the Nationals spent $210 million on Max Scherzer, but Zimmermann has left the door open for a new contract with Washington this spring. There's always the possibility he gets traded as well, if another club meets GM Mike Rizzo's asking price, but for now Zimmermann remains part of the Nats' extremely loaded rotation.