"We knew the potential was there for this," A's manager Bob Melvin said. "Unfortunately he had a couple different opinions but they all came up the same, that ne needed to have the surgery, so it's going to be a while."
Triggs was originally placed on the disabled list June 10 with a strained hip, his last start coming the day prior against Tampa Bay. He allowed a combined 20 earned runs in his final four starts, after holding opponents to 11 earned runs total in his first eight starts. Seven times in 12 starts overall, he yielded one earned run or fewer.
The converted reliever had made just six career starts prior to joining Oakland's Opening Day rotation in April.
"He got off to a great start," Melvin said. "Unfortunately it came to a close earlier than he would like. Now it enables him, whether he comes back as a reliever or a starter, he has the confidence knowing he can do it on both ends."
A's rotation plans on hold
Right-hander Jharel Cotton, stationed on the DL with a right thumb blister, is scheduled to throw a bullpen session on Sunday, at which point the A's will determine whether they can start him in next week's three-game series with the Rays.
Until then, they will wait to announce their rotation plans for the first two games of the series, with right-hander Daniel Gossett expected to start one of them. Should Cotton be unable to pitch, right-hander Chris Smith is likely to draw another start.
• Chad Pinder (left hamstring) is set to run the bases at the Coliseum on Saturday and, barring any setbacks, could be nearing a Minor League rehab assignment.
• Right-hander Kendall Graveman (shoulder) threw live batting practice in Arizona on Friday, putting him closer to a Minor League rehab stint.
• Reliever Ryan Dull (right knee) will throw a 30-pitch simulated game Saturday.
• Chris Bassitt will make his next rehab start with Triple-A Nashville on Sunday. The right-hander, working his way back from Tommy John surgery, is scheduled for three innings and 45 pitches.
• Catcher Ryan Lavarnway, who was designated for assignment last week, has been outrighted to Triple-A.
Jane Lee has covered the A's for MLB.com since 2010.