Valencia appeared to be shaken up on a play at the plate that concluded the top half of the frame, when he was called out on a spectacular 105.5-mph throw from left fielder Aaron Hicks for the back end of an inning-ending double play.
Melvin said the injury occurred not when Valencia was running home, but when he popped up from the plate.
By removing Valencia from the game, shifting Chris Coghlan from second to third base and opting to transition Jed Lowrie from designated hitter to second, Melvin lost his DH.
Leading, 3-1, at the time, Melvin said he would've chosen to play Mark Canha at third base and keep the DH intact only if the A's were behind.
"But when we're ahead and we have a ground-ball pitcher on the mound, we're gonna go ahead and stick with our best defense," Melvin said.
That pitcher, Kendall Graveman, found himself batting in Valencia's No. 4 spot in the batting order in the fifth inning as a result. With a runner on second and two outs, the Yankees intentionally walked Josh Reddick to get to Graveman. Facing Yankees starter Nathan Eovaldi, Graveman took a strike, fouled off the second pitch he saw and swung through the third to end the frame.
"I didn't show up to the park thinking I was going to get an at-bat," said Graveman, who was the first starting pitcher to bat at the current Yankee Stadium. "You realize that they [lost] the DH and you want to get deep in the ballgame, so to get an at-bat there was big because it means I was still in the game.
"It's one of those things, you're just trying to hit a fastball. … Maybe I had too heavy of a bat. [Josh] Phegley handed me his bat. Maybe I should've used [Billy] Burns'."
Jane Lee is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.