Washington have placed starting pitcher Tony Armas Jr on their injury list just five days before the start of their first MLB season.
Armas, who has a groin strain and Nationals general manager Jim Bowden said he is likely to miss four starts.
"The injury affects the team, but you can't push a pitcher with a groin injury or you'll lose him for the whole year," he said.
Armas suffered the injury in the first inning of a pre-season game on Sunday against the New York Mets.
The 26-year-old is set to be the number two man in Washington's rotation, behind Livan Hernandez.
Last season, Armas made just 16 starts, going 2-4 with a 4.88 ERA.
He has a career mark of 32-41 with a 4.21 ERA over six seasons.
A torn labrum in Armas' right shoulder limited him to five starts in 2003 and another shoulder injury did him in again for 2004.
He also missed 23 days of the 2002 campaign with a strained lower back.