Gallardo complained of a sore shoulder in his start Friday against the Kansas City Royals and was pulled after two innings and 45 pitches. The Orioles flew him back to Baltimore to be examined.
While Gallardo has made 30-plus starts in each of the past seven seasons, the Orioles were concerned about his shoulder after a February physical before signing him. They reconstructed his contract, cutting their original offer from three years to two with an option. The 30-year-old is guaranteed $22 million over two years, including a $2 million buyout for 2018.
Gallardo has been on the disabled list four times in his career, but never for an arm issue. The last time was 2010 with an oblique strain.
The Orioles activated left-hander Brian Matusz, who had been on the disabled list with a left side strain.