Lewis hit .262 with 11 homers and 28 RBIs last season, winning the American League Rookie of the Year award. He has been out of Seattle's lineup for most of this week after crashing into the wall during a spring training game against the Los Angeles Dodgers on Monday.
Manager Scott Servais said Saturday that the injury has not responded as athletic trainers had hoped.
"Based on where we're at, we're going to try to get that calmed down as quick as we can, hoping it's nothing more than that," Servais said. "But being this close to Opening Day, and again I just got this news a little while ago, we have to wait and see how it goes. Is he going to be available Opening Day? I'm not sure."
If Lewis isn't ready for the start of the season, the Mariners likely would shift prospect Taylor Trammell over to center field. Trammell seems likely to be the team's everyday left fielder to begin the season.
Servais also said general manager Jerry Dipoto might look outside the organization as players are released this week.
"If Kyle isn't able to be there when we open up, we may look to add from outside," Servais said. "I'm not quite sure where we head yet."