Speculation surrounding Sean Nolin's potential spot in the Oakland Athletics' starting rotation will have to wait after a concerning throwing session Saturday.

Manager Bob Melvin told reporters Nolin will be shut down for an unspecified amount of time after a flat-ground throwing session caused the 25-year-old pain. The soreness could be attributed to his offseason sports hernia surgery, according to John Hickey of the Bay Area News Group.

"He's still feeling a little tug," Melvin said.

Melvin indicated there's no timetable for his return and the injury has moved him further behind several other candidates on the Athletics.

Nolin arrived in Oakland from the Toronto Blue Jays during the winter as part of the trade that sent Josh Donaldson north of the border.

Nolin, who has 2.1 major-league innings to his name, registered a 3.50 ERA during 17 starts with the Blue Jays' Triple-A affiliate, the Buffalo Bisons, in 2014.