The Padres have yet to announce the extent of the injury, which took place in the 10th inning.
Tatis did an awkward-looking split while trying to stretch for a throw at second. He was not able to keep his foot on the base.
The 20-year-old laid on the ground for several minutes and attempted to get up and move around to stretch out his legs. He left the field while the play was under review. Umpires ruled that the runner was safe.
Tatis is hitting .300 with six homers and 13 RBIs. On Sunday, he had a career-high three hits and a stolen base in the eventual 7-6 Nationals win in 11 innings.