Gregg will make his first start since 2003 when the Angels resume their weekend series with the Kansas City Royals.
Escobar is expected to miss one or two starts after being placed on the DL on March 31 with a strained right elbow. Gregg went 5-2 with a 4.21 ERA in 55 relief appearances for the Angels last year. In his rookie season of 2003, Gregg was 2-0 with a 1.35 ERA in three starts.
He prepared for the emergency start by throwing 75 pitches during a Class A intrasquad game at Rancho Cucamonga on Monday.
Matching up with the Royals should be a settling influence for Gregg, who is 2-0 with a 2.89 ERA in three career appearances, including one start, against Kansas City.
The Angels had never completed a season-series sweep of an opponent prior to taking all seven meetings with the Royals last year.
But Kansas City struck back with a 6-2 win in Friday’s series opener as Denny Bautista pitched eight brilliant innings and Mike Sweeney drove in two runs in the first of nine meetings between the clubs this season.
Garret Anderson drove in both runs for the Angels, who opened the season by taking two of three from Texas.