Hill is expected to have the surgery in the next couple of days. Dr. Benjamin Shaffer, the team's physician and orthopedist will perform the procedure.
"Shawn should be 100 percent by Spring Training," general manager Jim Bowden said.
The forearm is not Hill's only injury issue. On Oct. 4, Hill is scheduled to have surgery on his left shoulder. He hurt the shoulder running the bases against the Marlins last April and it grew worse a couple of weeks later when he tried to make a play at first base against the Padres.
Hill eventually went on the disabled list in mid-May because the shoulder made his mechanics go out of whack and it ended up hurting his elbow. Hill missed three months of the season.
Hill last pitched on Friday against the Phillies, and he had his worst outing of the season. The Nationals were bested by the Phillies, 6-3, at Robert F. Kennedy Stadium. Hill, who lasted 4 2/3 innings, gave up all six runs on eight hits. It was Hill's shortest outing since he hurled 1 1/3 innings against the Pirates on July 9, 2004.
After the game, Bowden was in the locker room checking on Wily Mo Pena who suffered a right hand injury. Hill then spotted Bowden and told him that he had a problem with his forearm, which gave him problems during Spring Training.
Hill was scheduled to pitch against the Mets on Wednesday night at Shea Stadium, but left-hander Mike Bacsik will get the start instead.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.