Beltran remained in the lineup as the designated hitter, batting third, but was relieved of his duties in center field about an hour before the first pitch.
"During batting practice, I felt I was kind of tight," Beltran said. "I took treatment before I went out, but it's bruised. I don't know from what. I don't recall hitting myself in the knee."
Manager Jerry Manuel had planned on giving Beltran, David Wright and Gary Sheffield one game each at DH this series, the team's first in an American League park this season. Sheffield had originally been written into Friday's lineup as DH. Instead, Jeremy Reed moved from left to center field to replace Beltran, and Sheffield took over in left.
Feeling better throughout the game, Beltran said that he would attempt to play center field on Saturday but that he was unsure if he will be able to.
"It got better," he said. "It's not pain-free, but it got better."
Beltran had arthroscopic surgery on both knees following the 2007 season. He entered Friday's game hitting .279 in 34 career games at DH, mostly during his time with the Royals.
Anthony DiComo is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.