Outfielder Nick Martini, who was hitless in nine at-bats during his first stint with the A's, was optioned back to Nashville.
"Just something you have to deal with," A's manager Bob Melvin said. "When you're reluctant to put someone on the DL because you're going to lose them for 10 days, then other areas are going to suffer for it.
"It certainly wasn't anything Nick Martini did. We really like Nick. When you first get to the big leagues like that and get a couple games under your belt and don't get a hit, you feel like you did something wrong, but that's not the case. We like the quality of his at-bats, but unfortunately, someone had to get sent down at this point."
Cahill hurt his Achilles during running drills Thursday -- "He told me it felt like someone punched him in the Achilles," Melvin said -- but could be back on the mound within a week.
"Hopefully, each and every day, he gets a little better," Melvin said. "And hopefully we can push him in there somewhere four or five days down the road."
Worth noting • Lefty Ryan Buchter (left shoulder strain) threw 20 pitches to hitters in Class A Advanced Stockton on Friday night, putting him closer to a Minor League rehab assignment. The A's have been without Buchter since April 26.
Jane Lee has covered the A's for MLB.com since 2010. Follow her on Twitter @JaneMLB.