Earlier in the day, Sportsnet's Ben Wagner reported that the strain could result in Kirk missing up to six weeks.
Kirk appeared to tweak something while running out a foul ball against the Atlanta Braves on May 1. He remained in the game but was later removed for Danny Jansen. He was placed on the 10-day injured list the following day.
The 22-year-old is coming off a multi-home run performance against the Braves where he was set to earn more playing time. In 17 games this season, Kirk is slashing .225/.326/.475 with three home runs and five RBI.