OAKLAND, Calif. - Oakland Athletics closer Sean Doolittle is unlikely to be ready for the start of the season because of a slight tear to the rotator cuff in his left shoulder along with considerable inflammation and irritation in the area.

Doolittle had a platelet-rich plasma injection last Friday in an attempt to decrease the inflammation and irritation before he begins rehabilitation under the direction of athletic trainer Nick Paparesta, assistant general manager David Forst said Friday. There is no timetable for Doolittle's return, though doctors believe the left-hander will recover to pitch without needing surgery.

He started experiencing soreness last month while beginning his regular off-season throwing program. When the discomfort remained through a few throwing sessions, the A's sent Doolittle to their orthopedist in Arizona, Dr. Doug Freedberg. Doolittle had an MRI and, after consultation with Dr. Will Workman in Oakland, they diagnosed the rotator cuff tear and other issues. Then the pitcher had the PRP shot.

"Neither doctor in this case believes surgery is warranted," Forst said. "Both of them, and Nick, believe Sean pitched with this for some amount of time last season and all are confident he can do so again once the inflammation is gone and his strength returns."

The 28-year-old Doolittle made his first All-Star team last season. He went 2-4 with a 2.73 ERA and 22 saves in 61 appearances as Oakland reached the playoffs for the third straight year. He became the closer after 2013 AL saves leader Jim Johnson began the season in the ninth-inning role, struggled and was eventually released.

Doolittle spent Aug. 24 to Sept. 12 on the disabled list because of a strained right intercostal muscle.

Last April, Doolittle was rewarded with a five-year contract worth $10.5 million. He has been a reliable member of Oakland's bullpen since converting from first base late in the 2011 season.