One of Cleveland's top bullpen arms, Karinchak underwent an MRI on Thursday that revealed a mild strain in his right teres major muscle. The team said Karinchak has shown improvement but won't throw for up to 10 days before being reevaluated.
The Guardians open the season April 7 in Kansas City.
The hard-throwing Karinchak, who also has a devastating curveball, went 7-4 with a 4.07 ERA and 11 saves last season. Manager Terry Francona has used Karinchak in a setup role and as a closer.
Karinchak has pitched in 92 games over the past three seasons with Cleveland.
Also, Guardians backup catcher Luke Maile could be out for a month with a strained hamstring. Maile got hurt while running the bases in an exhibition game this week.