Los Angeles Angels ace Garrett Richards was carted off the field on a stretcher in the second inning at Fenway Park with a possible left patellar injury.
The team is awaiting further evaluations before announcing anything more definitive.
The Angels are facing the possibility of being without their best starting pitcher for the rest of the season.
With runners at first and second and one out, Brock Holt hit a grounder to the right of first baseman Albert Pujols. He fired the ball to Erick Aybar for the force, while Richards sprinted to first to receive the return throw. But just before reaching the bag, his knee collapsed underneath him. He clutched his left knee in agony while Angels trainers rushed to his side.
Richards remained down for several minutes while all the Angels players on the field gathered around him at first base, and Red Sox slugger David Ortiz came out of the Sox dugout and joined the group to show his support as they lifted the 26-year-old right-hander onto the stretcher.
Richards entered Wednesday’s start 13-4 with a 2.53 ERA and 164 strikeouts in 167 innings.
The Angels have already lost 23-year-old starter Tyler Skaggs to Tommy John surgery.