"Good arm ... has thrown the ball very well," said Giants manager Bruce Bochy. "He's the type of guy we think can help this club."
Mijares owns a 2.56 ERA in 38 2/3 innings this season. He's given up four earned runs over his last four outings, spanning an inning of work. That rough patch ballooned Mijares' ERA, but he'd given up one earned run in 22 games prior to stretch, dating back to May 30.
Bochy said Mijares will likely be used as a lefty specialist. Left-handers are batting .214 with 21 strikeouts in 84 at-bats against Mijares this season. Bochy added that having Mijares will free up more opportunities to use fellow left-hander Jeremy Affeldt in save situations.
Bochy said Mijares could possibly join the club in St. Louis as early as Tuesday.