ARLINGTON -- A sore right hamstring could prevent left-hander Erik Bedard from making his scheduled start against the Red Sox Saturday night at Safeco Field.

"He is a tentative scratch right now because of his hamstring," manager Don Wakamatsu said on Thursday. "We will talk further on who would fill that, but we would probably fill it internally and not make a roster move. That would probably be [Garrett] Olson."

Bedard, who missed nearly half of last season with various ailments, felt discomfort in the first inning of his start against the Twins last Sunday in Minneapolis. He was able to make it through 4 2/3 innings, and when his pitch count reached a season-high 110 pitches, he was replaced by Mark Lowe.

"He pitched through [his sore hamstring], everything warm and fuzzy because of the adrenaline and everything else," Wakamatsu said. "It was there and we kind of rested it. He tested it yesterday and feels that it doesn't warrant DL time, but we could either have him miss a start or push him back until it's healthy.

"Maybe we can juggle the rotation a little."

Bedard has pitched well in all seven of his starts this season, posting a 2-1 record and 2.53 ERA, which is the third-best in the American League. He has 43 strikeouts and 11 walks in 42 2/3 innings.

Wakamatsu said he was unaware of Bedard having a previous issue with the hamstring.

A final decision would be made on Friday, the manager said.

"We're already making tentative plans by the way we use our bullpen today," Wakamatsu said of the series finale against the Rangers.

Olson, acquired from the Cubs along with Ronny Cedeno for pitcher Aaron Heilman, pitched the 10th inning of Wednesday night's game and stood to be the winner if the Mariners had been able to hold on to their one-run lead in the 11th.

He has surrendered two earned runs in seven innings since being promoted from Triple-A Tacoma on May 6.

Meanwhile, left-hander Ryan Rowland-Smith reports to extended Spring Training in Peoria, Ariz., on Friday to continue rebuilding his arm strength following more than a month on the disabled list with triceps tendinitis.

After two outings in Arizona, he would then make two starts for Triple-A Tacoma before re-joining the Mariners' rotation at the end of this month.