"He has a shoulder problem but I don't think it's a big problem," Twins general manager Terry Ryan said. "I think he'll be all right."
The right-hander tossed five scoreless innings in his last outing to improve to 3-5 with a 2.42 ERA in 17 starts this year. The 19-year-old has struck out 58 and walked 23 in 81 2/3 innings.
Stewart was originally selected by the Twins as the No. 4 overall pick in the 2013 First-Year Player Draft.
Rhett Bollinger is a reporter for MLB.com. Read his blog, Bollinger Beat, and follow him on Twitter @RhettBollinger. This story was not subject to the approval of Major League Baseball or its clubs.