Stoudemire underwent a debridement -- a procedure that cleans out dead tissue or foreign material -- for his troublesome left knee. The surgery was performed by Knicks team doctors.
"It's tough," coach Mike Woodson said. "Amar'e is a big piece to our puzzle. I don't care how you slice it. We'll be here when he gets back. We just have to hold the fort down until he's able to get in uniform and on the floor playing."
The Knicks originally thought Stoudemire's injury, first surfaced in early October, was a bone bruise, and they listed him as day to day.
On Sunday, the team announced an MRI revealed Stoudemire had a ruptured popliteal cyst behind his left knee and would be out two to three weeks.
But ESPN The Magazine's Chris Broussard reported Monday night that after seeking a second opinion, it was determined Stoudemire would miss at least the first six weeks of the season, which the team confirmed Tuesday.
Stoudemire will be out until at least December 12, according to the Knicks' timetable, which means he'd miss at least the team's first 20 or 21 games, depending on when they make up their postponed opener against the Brooklyn Nets.
Any issue surrounding Stoudemire's left knee is a point of concern for the Knicks.
Stoudemire had microfracture surgery on his left knee in 2005. He recovered well from that surgery, but the knee is still viewed as vulnerable.
Most teams were scared off by Stoudemire's history of knee ailments during summer 2010, when he was a free agent. The Knicks signed the former Phoenix Suns player to a five-year, $100 million contract, but the deal was uninsured because of the condition of his knees.
After he was diagnosed with the ruptured popliteal cyst, Stoudemire went for a second opinion, consulting Dr. Thomas Carter, the Suns team doctor who performed the microfracture surgery.
With Stoudemire out, Woodson and the Knicks will rely heavily on Carmelo Anthony to carry the offense. Anthony may play power forward against smaller lineups.
When Stoudemire was out for 13 games late last season, Anthony thrived at power forward, earning a player of the month award. The Knicks went 9-4 during that stretch.
Against bigger lineups, Woodson may opt to start veteran Kurt Thomas at power forward.
Anthony expressed disappointment over Stoudemire's injury. Some critics have argued that Anthony and Stoudemire are a bad fit together in New York. Anthony said on Monday that he hoped, for the first time in his New York tenure, to be able to play an 82-game season with Stoudemire.
"It's disappointing. I definitely thought that this was going to be the season that we had a chance to go out there and play together in a full season (with) no injuries, but at the end of the day, you can't control what happens to your body, you can't control injuries," Anthony said. "We just want him to be healthy."
Stoudemire is coming off a difficult 2011-12 season in which he suffered through the death of his brother, a back injury late in the season and a hand injury after he punched the glass encasement of a fire extinguisher after a Knicks playoff loss to Miami. Early in the preseason, he expressed optimism about bouncing back this year.
"I know how hard Amar'e has worked this summer, so I feel for him," Tyson Chandler said. "... But like I told him, it's a little setback in the big picture. In the big scheme of things. It's a minor setback."
The Knicks face a rough early schedule without Stoudemire. Their first eight games are against teams that made the playoffs last season.
Ian Begley is a regular contributor to ESPNNewYork.com.