ST. PETERSBURG -- Mookie Betts exited with a right thumb contusion in the fifth inning of Sunday's 3-2 loss to the Rays. X-rays came back negative, and he is listed as day to day, the team announced.
The injury occurred in the fourth inning after Betts hit a grounder to third baseman Trevor Plouffe. Plouffe's throw pulled Lucas Duda off the bag backward toward the first-base dugout, and Duda reached to apply the tag on Betts. Betts ducked to avoid the tag, which caught him atop the head and knocked off his helmet. His helmet fell and landed on his thumb.
Rajai Davis replaced Betts in right field in the bottom of the fifth, after Betts had played another inning in the field. Manager John Farrell said the Red Sox removed Betts as a precaution, as the right fielder has been dealing with nagging soreness.
"It's been going on for a couple months, but I was able to just kind of play through it," Betts said. "But today I ended up hitting it kind of hard, I think it was on my helmet. My helmet came off and hit my thumb, and I wasn't able to really hold a bat."
No one in Boston's lineup has been more important than Betts. The 24-year-old came in second in American League Most Valuable Player Award voting last year and has led the team's position players in Wins Above Replacement in each of the past three years.
Betts was in the midst of a surge at the plate recently, batting .306 with 12 RBIs in his past 11 games heading into Sunday. Nine of his 15 hits over that time went for extra bases, with four home runs.  He said he does not expect the thumb injury to keep him out long. 
"I should be all right to play [Monday]," Betts said. "Just have to find a way not to hit it."