Ackley suffered the injury on Saturday while diving for an Alfonso Soriano line drive into center field. His glove caught into the ground and bent back along with his thumb.
The Mariners are fortunate that Ackley merely suffered a strain. He will likely only miss a few days with the injury. Had he broken the thumb, he may have missed a month.
Seattle recently converted Ackley to the outfield after he spent nearly his entire professional career at second base. Saturday's game was just his second major league game in center field.
Ackley, 25, has hit just .202/.261/.245 this season and had been sent to the minors in the hopes he could straighten out his hitting and learn the outfield. He was called up on June 25 when Franklin Gutierrez was placed on the disabled list with a strained right hamstring.
Seattle has been dealing with a rash of injuries in their outfield recently. Both Gutierrez and Michael Morse are on the disabled list while Michael Saunders is dealing with a finger injury of his own.