Gentry was hit by a pitch from A's pitcher Jarrod Parker in the seventh inning. Gentry stayed in the game and even stole second base after getting hit by the pitch. He also played defensively in Thursday's 4-3 victory but he has not been able to swing a bat.
X-rays did not reveal the fracture. But when the hand did not improve, Gentry had an MRI on Saturday that revealed the fracture.
"I have been trying every day to take some swings and see how it feels," Gentry said. "It wasn't feeling good. It was one of those fractures, if you had done 100 X-rays, it wouldn't have shown up. We needed an MRI."
Engel Beltre was called up to replace Gentry after hitting .300 with four home runs, 21 RBIs, 44 runs scored and 13 stolen bases for Triple-A Round Rock. He was 17-for-33 in his last seven games, but he was shocked when he got the call on Saturday night.
"It was the biggest surprise of my life," said Beltre, who was one of three players along with outfielder David Murphy and pitcher Kason Gabbard acquired from the Red Sox on July 31, 2007, for pitcher Eric Gagne.
Beltre has been playing center field primarily for Round Rock but he can play all three outfield positions.
"He plays hard, has a good bat, can run and play defense," manager Ron Washington said. "I'll find some playing time for him, but he's not going to unseat [center fielder Leonys Martin]."
T.R. Sullivan is a reporter for MLB.com. Read his blog, Postcards from Elysian Fields, and follow him on Twitter @Sullivan_Ranger. This story was not subject to the approval of Major League Baseball or its clubs.