Seattle manager Scott Servais said Tuesday that an MRI revealed the extent of the injury. Hernandez was placed on the 10-day injured list on Sunday and was originally diagnosed as having a shoulder strain. Servais said the injury is similar to the lat strain suffered by Hunter Strickland early in the season, just not as severe.
Hernandez landed on the injured list a day after he pitched 2 1/3 innings against Boston, giving up six hits and seven earned runs in his second-shortest start of the season. Hernandez lasted only one inning in April against Kansas City, but left that game because of an illness.
Hernandez said he's hopeful he will be out only a couple of weeks.