Maxwell was substituted in the first quarter of Collingwood's 86-point win over St Kilda at Etihad Stadium on Friday night with a calf strain, while Karnezis strained a hamstring at training earlier the same day.
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Sidebottom was reported for engaging in rough conduct against St Kilda's Maverick Weller in the opening seconds of the match, with Weller later substituted in the first quarter with concussion.
Collingwood coach Nathan Buckley said after Friday night's game that Maxwell and Karnezis were facing about three to four weeks on the sidelines.
"Maxy's done his calf, Patty Karnezis did his hammy today at training, we've lost a few with soft tissue (injuries) and the report," Buckley said.
"But that's footy. That's life in an elite environment at the top level, you're looking for that improvement constantly and that's why we have 45 players on a list and we work to develop the depth of it.
"We're going to need it (depth) next week."
Buckley said it was particularly disappointing that former Brisbane Lion Karnezis had been injured when his recent form in the VFL suggested he was close to making his Collingwood debut.
"He's had a really good month of footy and probably what it shows is that he still had a few more (games) to go in regards to getting back to full football fitness," Buckley said.
"It's disappointing for him because he's put a power of work in through the pre-season, (he) really didn't get out onto the track or train with the boys until quite late, February really.
"He's settled into the club really well. He's played his role particularly well at VFL level, so the challenge for him is going to be to keep going back, strengthening his body, getting back to football fitness and getting himself in a position where he can contend for AFL and be able to run four quarters out at AFL level."
In better news for the Magpies, Buckley said their two late withdrawals from Friday night's game, Dane Swan (sore heel) and Brodie Grundy (tight back), along with Luke Ball (calf), should return for Collingwood's Queen's Birthday clash with Melbourne on Monday week.
Buckley said Friday night's win was the Magpies' first four-quarter performance of 2014.
"Most of our players in a quick review there thought they were able to tick off the areas that they needed to, the areas we focused on," Buckley said.
"We thought most of our individuals contributed over the four quarters.
"We've had some really strong three-quarter performances this year, but that's the first four-quarter performance we've put in."
