Etherington, a graduate student who will be eligible to play right away after transferring from Indiana, suffered a torn ligament during a summer workout.
"It's a tough blow for Austin, but we're glad that the surgery went well," said Butler head coach Brandon Miller. "He's overcome adversity in the past, and we're confident that he will make a full recovery. We're looking forward to his return, and we're excited about the contribution he'll make to our program this season."
Etherington was granted a medical redshirt as a sophomore after missing all but seven games due to a torn ACL. He averaged 2.0 points and 1.6 rebounds in 10.6 minutes a game for the Hoosiers last season.
The Cicero, Ind. native is one of two transfers to join Butler this offseason, along with former N.C. State point point guard Tyler Lewis, who will not be eligible until the 2014-15 season due to NCAA transfer rules.
The Bulldogs finished 14-17 last season — their first in the Big East after leaving the Atlantic 10 — under first-year coach Brandon Miller, who replaced current Boston Celtics head man Brad Stevens.
-- Chris Johnson