Mengden will follow opener Liam Hendriks against the Orioles on Wednesday, Jane Lee of MLB.com reports.
Mengden will cover the bulk of Wednesday's innings. He's made three long-relief appearances this season, posting a 2.53 ERA, 1.22 WHIP and 6:3 K:BB across 10.2 innings. It's unclear if he'll continue to work out of the bullpen down the stretch or if he'll rejoin the rotation at some point.