A’s slugger Matt Olson left Thursday’s 5-4 loss to the Mariners in Tokyo in the sixth inning with right hand pain. The first baseman will be re-evaluated when the team returns to Oakland.

Olson told reporters that the injury occurred while he was batting in the fifth and fouled off a slider from Mariners pitcher Yusei Kikuchi. Olson singled later in the at-bat and ran the bases before he was replaced by Mark Canha before the top half of the sixth.

“Just felt pain pretty much on contact,” said Olson. “I was trying to shake it out the rest of the at-bat, and I’m sure that hitting it on the barrel helped, but once I got on the bases and some time passed, the pain started feeling worse and I just didn’t have any grip.”

Olson is a key piece of an A’s club looking to build on their surprise run to the American League Wild Card Game in 2018. He won his first Gold Glove Award for his defense at first base last year while slugging 29 homers and ranking among the league leaders in hard-hit rate, per Statcast.

“Anytime he comes out of the game, there’s some concern,” said A’s manager Bob Melvin. “He’s a pretty tough guy. Played 162 games last year. It was on one swing. A couple swings before his hit, but I could see him shaking his hand after, and he kept shaking it.”

Oakland returns to the United States with an 0-2 record after a pair of close losses to Seattle. The A’s will play their Bay Area rivals, the Giants, in three straight exhibition games beginning Sunday before playing their home opener against the Angels on March 28.