i'd like to understand what do they mean by "(he) was vulnerable because he has minor league options remaining" in the following story:
ST. LOUIS (AP)—The Milwaukee Brewers optioned left-handed reliever Mitch Stetter to Triple-A Nashville on Tuesday, making room on the roster to activate Jeff Suppan to start against the Cardinals.
Stetter was 2-1 with a 2.78 ERA in 23 appearances over two stints. He has held opponents to a .160 batting average, and went 1-0 with a 1.74 ERA since recalled on June 20, but was vulnerable because he has minor league options remaining.
Manager Ned Yost said the pitcher understood, and said “There wasn’t a lot of things we could do.”
The move left Brian Shouse as the lone left-hander in the bullpen, limiting Yost’s late-inning flexibility. Shouse was 1-1 with a 4.50 ERA in 29 games.
