Leading off against Boston's Andrew Miller, Tabata laid a bunt down the third-base line. He got to first about the same time as Kevin Youkilis' wild throw, and after finishing a few more strides past the bag, Tabata fell to the ground. He never got back up.
Tabata, who was seen limping but also walking without assistance after the game, said he suffered the injury after he touched first base.
Both of the Pirates' trainers, as well as manager Clint Hurdle and first-base coach Luis Silverio, hurried out to Tabata, who remained on the ground for several minutes. He was eventually placed on a stretcher and carted off the field.
Asked afterward about the injury, Tabata said he wasn't sure how severe it might be. He did add that he was feeling "better" already.
Tabata will undergo additional testing on Monday, after which the team is expected to issue an update. It is not yet a given that Tabata will land on the disabled list, which already has nine players on it.
Tabata has become Pittsburgh's primary leadoff hitter and entered with a .287 batting average in June.
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.