An MRI exam revealed that Chavez, who had to be carted off the field following a collision with shortstop Yuniesky Betancourt during Friday's game against Arizona, has a significant ACL tear in his right knee and will miss the remainder of the season.
Manager Don Wakamatsu said Chavez will have surgery once the swelling goes down, and could be looking at a six-month absence.
"There's quite a bit of damage," Wakamatsu said. "Without making a mistake on the diagnosis, there's a couple different tears. It's a bad one."
Mariners team doctor Ed Khalfayan said that Chavez could be out nine months to a year. That time frame would mean Chavez wouldn't be ready to go for the Mariners' 2010 opener, but Khalfayan said he thinks Chavez has a good chance of being 100 percent by the time he returns to action.
As for Spring Training, that seems to be a long shot at this point.
"I think he would be limited in what he could do," Khalfayan said. "If we get him back in nine months, we would be doing well. Age is in his favor."
With Chavez on the disabled list, Seattle activated infielder Josh Wilson, who was claimed off waivers on Friday. Wakamatsu said that Wladimir Balentien, who has struggled this season in limited playing time, will have the chance to prove himself in left field. But Wakamatsu added that Ken Griffey Jr. may also see more time in the outfield, and that Ronny Cedeno will become the team's backup center fielder.
Recent callup Mike Carp, a first baseman who was also looked at in Spring Training as an outfielder, may also get a look in left field in an attempt to add depth.
"I think a lot of it is going to depend on Balentien," Wakamatsu said. "We've given him a couple different opportunities this year to be the player we think he can be. If not, we'll have to make some changes."
Betancourt caught the ball on the play and was not injured. Chavez took the brunt of the collision on his knee, and may have worsened the damage when Betancourt rolled back onto it.
"It was just one of those weird instances," Wakamatsu said. "You try to say one goes high, one goes low, but it's just kind of a Bermuda triangle out there."
Chavez was batting .273 with nine stolen bases this season. He was one of 12 players involved in the three-way trade between the Mariners, Mets and Indians at the Winter Meetings in Las Vegas in December.
Christian Caple is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.