Betts said he's been dealing with the issue the "last couple of days" and that he felt it Friday after throwing Minnesota Twins second baseman Brian Dozier out at second in the top of the fourth inning.
Betts was removed from Friday's game for precautionary reasons before the top of the fifth and was replaced by Michael Martinez.
"[I feel] pretty good today," Betts said. "Have to go for the treatment, make sure everything is clear before I get back out there."
Betts said the treatment has mainly consisted of icing his knee in order to get the swelling down.
Red Sox manager John Farrell said that Betts might need a couple of days to return, but "everything points to this being a short-term situation."
Betts has appeared in all 94 of Boston's games this season, batting .307 with 20 home runs, 63 RBIs and a league-leading 221 total bases. He hit leadoff homers against the Twins on Thursday and Friday, becoming the fourth player in the modern era (since 1900) to hit leadoff homers in back-to-back games multiple times in a single season (also on May 31 and June 1).
With Betts missing time, Farrell said that he'll have to pay close attention as to when to give his players days off so that he isn't without several of his top hitters at once.
"You always want to be in there and play," Betts said. "We have a pretty good team and I think everything is going to be fine. Hopefully I can get back in there quick."