After examining Guillen Friday morning by hand specialist Dr. Edward St. Mary recommended surgery. The National said on their Web site they will seek a second opinion to confirm the diagnosis.
"This is a devastating blow to the team," said General Manager Jim Bowden. "Good teams overcome adversity. Players in the organization will get the first opportunity to replace him, although we will look outside (the organization)."
Guillen apparently hurt himself during a weight-lifting session last month. He said the pain grew more intense after he took his first batting practice of the spring on Wednesday.
The team already has lost pitcher Brian Lawrence for the season because of surgery on a torn rotator cuff and torn labrum in his right arm and shoulder.
Guillen was Washington's best power hitter in 2005, when he hit 24 home runs.