SEATTLE (AP) — Mariners starter Felix Hernandez is expected to miss four to six weeks after being diagnosed with a lat strain in his right side.

Seattle manager Scott Servais said Tuesday an MRI revealed the extent of the injury. Hernandez was placed on the 10-day injured list Sunday and was originally diagnosed as having a shoulder strain. Servais and Hernandez said the injury is similar to the lat strain suffered by closer Hunter Strickland early in the season, just not as severe.

"(It's) grade 1, so it's not a big deal," Hernandez said before Tuesday night's game with the Oakland Athletics.

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.

The news comes as starter Wade LeBlanc prepares to return to the rotation. LeBlanc was in the clubhouse Tuesday after completing a five-inning, 60-pitch minor league outing Monday in Las Vegas. Servais said LeBlanc likely figures into the rotation in the near future but that nothing is set for the series against the Minnesota Twins this weekend. With a day off Wednesday, the team could move other pitchers around, as well.

LeBlanc, who was placed on the injured list April 14 after straining his right oblique, said he has felt no pain during his rehab and is ready to return to the rotation.

"I'm always ready to go," LeBlanc said. "Whenever they want to give me the ball, I'll take it."