Mariners manager Scott Servais said Thursday that Dunn (shoulder) has fallen behind Justus Sheffield (forearm) in their respective rehab programs, Shannon Drayer of 710 ESPN Seattle reports.
The two starting pitchers were placed on the 10-day injured list within a couple weeks of one another; Dunn landed on the shelf on June 18 with a right shoulder strain, while Sheffield was shut down July 7 with a left forearm strain. Coming out of the All-Star break, Dunn appeared to be closer of the two to returning, but his timeline was pushed back after he failed to complete a bullpen session during the Mariners' series with the Rays earlier this week. Even if Dunn is able to get back on the mound within the next few days, he'll still need to progress to facing hitters, and then complete a one- or two-start rehab assignment in the minors before the Mariners entertain bringing him back from the IL. Dunn doesn't look like he'll be ready to go until late August, in a best-case scenario.