With no outs and a runner on first base, Minnesota left-hander Francisco Liriano unleashed a 92-mph heater that tailed high and inside, striking Buck hard on the helmet. Buck immediately dropped to his knees, and was clearly shaken up.
After a brief meeting at home plate, Buck walked off the field with one of Cleveland's trainers. Utility man Luis Valbuena entered the game as a pinch-runner for Buck, who was in the lineup as the ninth hitter and left fielder.
Buck was later diagnosed with a head contusion.
"There's no signs of concussion," Indians manager Manny Acta said.
Acta was not sure if Buck would be available for Wednesday's series finale in Minnesota.
"We don't know yet," Acta said. "We're going to have to wait and see."
On the season, including Tuesday, Buck is hitting .243 with two home runs and 18 RBIs in 44 games for the Indians. He has been serving as the Tribe's primary right fielder with Shin-Soo Choo on the 15-day disabled list with a broken left thumb.
Buck started in left on Tuesday in place of Michael Brantley, who was a late scratch from the lineup due to an upset stomach. Cleveland is also currently without center fielder Grady Sizemore (right knee injury).
Acta added that Brantley was not an option off the bench.
"He's very sick," Acta said. "He couldn't hold any food last night or this morning, for that matter. He didn't look very good at all from the moment he showed up here. They gave him treatment the whole afternoon.
"We waited up until right before the ballgame, and still he was not in any type of condition to play. He was seen by the doctors, and we just kept him inside the whole time."