Cobb was pitching in the fifth inning of Saturday's game against the Kansas City Royals when he was struck in the head by a line drive off the bat of the Royals' Eric Hosmer.
Cobb lay motionless on the mound for several moments but was conscious as he was taken off the field on as stretcher.
After being taken to Bayfront Medical Center, he was diagnosed with a mild concussion.
The Rays said the 25-year-old hurler was to be released from the hospital Sunday, and the pitcher wrote on his Twitter account he was suffering only a minor headache.
Cobb has compiled a 6-2 record with a 3.01 earned run average in 13 starts this season, establishing himself as one of Tampa Bay's most dependable pitchers.