Slaten threw a bullpen session prior to Sunday's game against the Diamondbacks, Jen McCaffrey of The Athletic reports.
Slaten began a rehab assignment Friday for Double-A Portland, in which he exhibited shaky command, and Sunday's session was to address those issues. Boston manager Alex Cora told MLB.com that Slaten will most likely be with the Red Sox "in the upcoming days." That could mean at least one more rehab appearance for the right-hander.