Chavez will undergo an MRI on Saturday, Wakamatsu said.
"He looked like he hurt it pretty bad," Wakamatsu said. "They think it's going to be ligament."
The two fielders converged on a popup hit by D-backs designated hitter Felipe Lopez in the fifth inning of a 4-3 victory. The two defenders collided and Chavez went head-over-heels, hitting the ground hard and awkwardly. He immediately grabbed his knee.
Wakamatsu said they will discuss on Saturday what their plans are for the left-field position going forward. An obvious replacement candidate would be Wladimir Balentien, who took Chavez's place after the injury.
Betancourt caught the ball on the play and was not injured. He remained in the game. Chavez had to be taken off the field on a motorized cart.
"The guy busts his butt and he's giving it his all out there for me," Mariners starting pitcher Jarrod Washburn said. "Coming in, trying to make a play, giving it everything he's got. You feel bad for the guy. It breaks your heart when it happens to a teammate like that, or anyone. You hate to see people get hurt."
Chavez was one of the 12 players involved in the three-way trade between the Mariners, Mets and Indians at the Winter Meetings in Las Vegas in December.
He was 1-for-2 in the series opener against the D-backs, reaching on a single in the fourth inning, and stole his ninth base of the season.
Christian Caple is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.Less