The Nationals acquired Granillo from the Cardinals on Tuesday in exchange for George Soriano, Jeff Jones of the Belleville News-Democrat reports.
Granillo broke into the big leagues in 2025 with a 4.71 ERA and 18:7 K:BB over 21 innings. The 25-year-old has a career 31.9 percent strikeout rate in the minors but has also walked batters at a 12.7 percent clip. Granillo will compete for a spot in the Nationals' bullpen but does have minor-league options remaining.