Dunn is slated to serve as the Mariners' opening pitcher in Tuesday's game against the Astros.
Dunn will pick up his third MLB start after tossing two shutout innings while opening in front of primary pitcher Tommy Milone on Sept. 18 in Pittsburgh. The rookie is likely in line for a two- or three-inning appearance Tuesday while Milone covers the bulk of the innings again out of the bullpen.