Gsellman was optioned to Triple-A Las Vegas on Saturday, Matt Ehalt of The Record reports.
Gsellman turned in one of his best outings of the season earlier this week, giving up one run in 6.1 innings against the Diamondbacks, but he wasn't as sharp Saturday against the Nationals. With Seth Lugo (shoulder) ready to return, Gsellman will lose his spot for now. Look for him to return when rosters expand, and chances are Gsellman will get more starting opportunities in September.