CINCINNATI -- Home-plate umpire Jerry Layne had to exit Friday's Twins-Reds game in the fourth inning, after being struck in the head by a broken bat.

Devin Mesoraco was batting with one out in the bottom of the fourth when he hit a ground ball on a pitch from Nick Blackburn. Mesoraco's bat snapped at the handle, with the barrel hitting Layne flush on the side of the head. Layne went down immediately, as Mesoraco grounded out to the shortstop.

Trainers from both the Reds and Twins attended to Layne, who was down for several minutes but able to walk off of the field under his own power. He was examined by Reds medical director Tim Kremchek, and taken to Good Samaritan Hospital for X-rays and an MRI. Tests came back normal.

"He has a very sore area on his face," said Randy Marsh, Major League Baseball's director of umpires.

Layne does not wear a hockey goalie-style helmet, which is optional. He does wear the traditional mask, however.

"That's one of the things that can happen," said Marsh, who was watching the game from the Great American Ball Park press box. "You get hit on the side of the head and there's nothing to protect you there. He took a good shot."

At no point did Layne lose consciousness, Marsh said.

"When he went down, he didn't know what hit him. He didn't know if it was the ball or bat," Marsh said.

Layne, the crew chief and a 23-year veteran MLB umpire, was replaced by second-base umpire Bob Davidson. Play resumed after a 10-minute delay with the three remaining umpires. Despite the normal test results, Marsh later revealed that Layne would not work the rest of the series. He will be replaced by Mark Lollo.