OAKLAND -- Felix Hernandez is expected to miss three to four weeks with bursitis in his right shoulder, the Mariners announced Tuesday, after the veteran right-hander underwent an MRI test on Monday.
"Obviously disappointed to lose Felix," manager Scott Servais said. "We certainly need him in that rotation. We're going to be playing a lot of big ballgames here in September, and we'd love to get him back in that mix at that time.
"He's going to have to work his tail off, get the arm strength back. Hopefully it won't be that long, but three to four weeks is a little bit of a blow there."
The Mariners have 7 1/2 weeks remaining in the regular season, and they open a two-game series in Oakland on Tuesday night sitting one game back of the Royals and Rays for the American League's No. 2 Wild Card spot with a 57-56 record.
The Mariners are already without veteran right-hander Hisashi Iwakuma, who has missed the past three months with a shoulder issue, and lefty Drew Smyly, who had Tommy John surgery and didn't pitch a game this season. Seattle has used 15 starting pitchers -- the most in the Majors.
Rookie left-hander Marco Gonzales was called up from Triple-A Tacoma to replace Hernandez, and he gave up seven hits and five runs in a four-inning no-decision in his Mariners debut on Sunday in an 8-7 win in Kansas City.
This is just the fifth time in his 13-year career that Hernandez has been on the disabled list, and three of those trips have come in the past two seasons. He missed four weeks in 2007 -- his third year in the Majors -- with a strained right elbow and 2 1/2 weeks in '08 with a sprained ankle.
Since turning 30, things haven't gone quite as smoothly, however. Hernandez sat out seven weeks last season with a right calf strain, and he missed two months earlier this year with the same bursitis diagnosis in his right shoulder, something Servais hopes doesn't happen again.
"We don't quite have eight weeks left, so hopefully we can speed up the healing curve there a little bit," Servais said. "Felix is doing all the exercises and doing what he can to get back as soon as he can. He's going to be really important for us."
Hernandez had his string of eight straight seasons of 200-plus innings -- and 10 consecutive with 190-plus innings -- snapped last year when he was limited to 25 starts and 153 1/3 frames, going 11-8 with a 3.82 ERA.
This year, Hernandez is 5-4 with a 4.28 ERA in 73 2/3 innings over 13 starts. Though he's lowered his walk rate and increased his strikeout rate back to his career norms, he's still posted his highest ERA since 2006, highest WHIP since '08 and highest homer rate in his career.
Hernandez, a six-time All-Star, won the AL Cy Young Award in 2010 and owns a career record of 159-113 with a 3.19 ERA in 372 starts. He has two years and $54.7 million remaining on the seven-year, $175 million contract extension he signed in 2013.