Aardsma is eligible to come off the 15-day disabled list as soon as he's ready, but manager Eric Wedge said he'll likely need three or four Minor League outings to determine his availability.
The 29-year-old had 69 saves for Seattle over the past two seasons. Hopes for a two-inning simulated game effort in Kansas City over the weekend were postponed by bad weather, so Aardsma threw in the bullpen in Kauffman Stadium on Saturday and had a session of long toss in the outfield on Monday at Safeco Field.
"Assuming everything goes well today, we'll send him to Tacoma tomorrow and take it from there," Wedge said. "He'll probably need 3-4 outings, somewhere in that time frame. But that's always subject to change. We have to see how tomorrow goes, first time out, and go from there."
Wedge said he wouldn't be used initially in a closer's role in Tacoma, nor will he be brought out to start the first inning, as some clubs do so they can control the warmup situation for rehabbing relievers.
"He'll come in later," Wedge said. "I don't think he wants to do that, and it's better for him to be sitting out there, get that adrenaline kick and go out and pitch."
Brandon League has held down the Mariners' closer role so far this season, going 3-for-3 in save situations and posting a 4.76 ERA in six appearances.