A frustrating season continues to grow more frustrating for Toronto Raptors small forward DeMarre Carroll.

The Raptors' biggest free-agent acquisition this past summer underwent arthroscopic surgery on his troublesome right knee Wednesday morning, the team announced.

There is currently no timetable for his return, but head coach Dwane Casey expects it to be an extended absence.

casey on severity of demarre's injury: not a week to week thing, definitely will be longer term. — alex (@steven_lebron) January 6, 2016

I wouldn't expect a tonne of detail on Carroll's knee; early indications are 8wks as the window for his return, but things change. — Michael Grange (@michaelgrange) January 6, 2016

Mixed signals on whether Carroll will be back this season. Lowry defiantly to me: "He's not out for the season." — Ryan Wolstat (@WolstatSun) January 6, 2016

Carroll missed time early in the season due to a bout of plantar fasciitis - a painful and persistent foot ailment - before suffering a knee contusion in early December that sidelined him for nine games.

He returned to play five games after the three-week layoff, but still didn't seem to be operating at or even close to 100 percent. On top of struggling badly with his offensive efficiency (his true shooting percentage is down to a woeful 48.5 percent from last season's sterling 60.3), Carroll has been a step slow at the defensive end, which is, more than anything, where the Raptors paid him handsomely to produce.

After failing to help contain Chicago Bulls swingman Jimmy Butler as Butler went off for a franchise-record 40 second-half points Sunday, Carroll admitted to playing hobbled.

"I'm going to be quiet with what I really want to say. I take it on myself but I know I'm not all the way there," he said, according to Raptors Republic's Blake Murphy. "I don't want to speak too much but I'm not all the way there. And (Butler) did what he's supposed to do against a guy who's not all the way there."

The Raptors subsequently sat Carroll against the Cleveland Cavaliers on the second night of a back-to-back Monday, and the 29-year-old again indicated how badly he's been hampered.

"I don't want to say too much," he said, according to The Star's Chris O'Leary, "but at the same time man, only if you knew, you know what I mean? Only if you knew. It's one of those things."

Those physical struggles have been reflected in the numbers, both in Carroll's obvious offensive falloff and the fact the Raptors have been 4.1 points per 100 possessions better overall with him on the bench.

The team has offered no word on the specifics of the surgery or the extent of the damage to Carroll's knee.