Kowar was optioned to Triple-A Omaha on Monday, Anne Rogers of MLB.com reports.
Kowar got lit up for seven runs after entering out of the bullpen during Sunday's 17-3 loss to the Guardians, giving up 11 hits and walking one while striking out four over 3.1 innings. Manager Mike Matheny said that the 25-year-old will be a part of the starting rotation with Triple-A Omaha moving forward. In a corresponding move, Joel Payamps will rejoin the big-league club following an absence due to a family emergency.