That leaves Dan Straily on track to start Wednesday, having also garnered one extra day of rest, and Friday starter Brandon McCarthy in line to go again Thursday on five days' rest. Should he be unable to do so, if he experiences more issues with his right shoulder, Blackley could go again in his spot.
"We've been looking for a way to try to give Parker and Milone a little bit of a break," A's manager Bob Melvin said. "We are very cognizant of the workload of our younger pitchers, and we feel like this is a good time to be able to give them a little bit of a break, refresh them going forward for the rest of the season.
"It's a mental grind once you get to this time of the year. Tommy's last few games haven't been his best, but it really isn't about that. We've been looking to potentially do this for a while now, and with the two off-days and McCarthy coming back and the way Travis has pitched for us, this worked out very well timing-wise. It's about giving them a break."
Milone, already up to 140 1/3 innings this season, acknowledged his struggles on Friday in Chicago, and he referenced a similar stretch last season that was helped along by extra rest. The lefty has allowed at least five runs in each of his last three starts, after giving up more than one just twice in his previous six outings, twice not surrendering any.
"I had a couple of rough starts in a row around this same time last year, and they felt it was probably a good idea for me to rest because I hadn't skipped or missed a start before," Milone said. "After that, I came back and felt a lot better.
"For me to be pitching the way I am is obviously frustrating, and it could be a mechanical thing, just because I'm trying to fix things to make it how I want them to be, and rest may be just what I need, rather than changing things. I can definitely tell there's a difference when I'm out there. The pitches I'm throwing are just off. I feel the same, but it's just not coming out the same."
Parker, meanwhile, has gone 2-3 with a 5.94 ERA since sitting with a 5-3 record and a 2.46 ERA on July 2. Time off should also serve him well, and the team's ability to give that to him speaks volumes about its depth. Rehabbing hurlers A.J. Griffin and Brett Anderson are also expected back soon.
"We wouldn't be able to do this without the depth," Melvin said. "It means we have depth in starting pitchers a lot of teams don't have and we have confidence in quite a few of them and rightfully so."