Gray threw nine shutout innings for the A's on Sunday, ruling him out for Tuesday's All-Star Game.
Santiago last pitched on Friday. The 27-year-old is 6–4 with a 2.33 ERA and 1.098 WHIP this season for Los Angeles. He is third in the American League in ERA and eighth in WHIP.
This is Santiago's first career All-Star selection. Gray's selection was also the first of his career.
On the National League side, it was announced on Sunday that Los Angeles Dodgers pitcher Clayton Kershaw will replace Washington Nationals pitcher Max Scherzer on the NL All-Star roster. Like Gray, Scherzer pitched on Sunday.
The 2015 All-Star Game will be held on Tuesday at Great American Ballpark in Cincinnati.
- Molly Geary