Chandler left Tuesday's game against Charlotte in the first quarter after suffering the injury during a collision with Bobcats point guard Kemba Walker.
Tests Wednesday showed the fracture.
The Knicks say Chandler, the NBA's Defensive Player of the Year in 2011-12, did not suffer any ligament or nerve damage and will not need surgery.
Chandler is arguably the second-most important Knick, behind Carmelo Anthony, and the team will be hard-pressed to fill the void.
The Knicks have Kenyon Martin, Amar'e Stoudemire and Cole Aldrich as possibilities at center. Coach Mike Woodson had wanted to use Stoudemire and Martin in a platoon in an effort to keep both healthy for late in the season.
Both Martin and Stoudemire have been on a minutes restriction, with Stoudemire being brought along slowly due to knee issues. Martin, 35, now could see more minutes than anticipated.
Chandler has averaged 7.3 points and 9.0 rebounds in four games. He had five blocks in the season-opening win over Milwaukee and 19 rebounds and four blocks in a loss to Chicago.
Woodson said that with Chandler out, he may start a small lineup that consists of Bargnani at center with Anthony at power forward. Raymond Felton and Pablo Prigioni would start in the backcourt, with Iman Shumpert at small forward. J.R. Smith will be available when the guard returns from suspension on Sunday.
Woodson said he wants to keep Martin's minutes between "10 to 20" moving forward.
"That's really the only route I have right now because of the fact that Kenyon and Amar'e are both on restricted minutes," Woodson said of going small.
"All we can do is nurse [Chandler] back. It's going to be a four- to six- week process and then welcome him back with open arms, because at the end of the day he is a big piece to what we're doing. He was the reason why we had the success we had in the last two seasons and we are going to need him in a uniform soon."
Ian Begley is a regular contributor to ESPNNewYork.com. Information from ESPNNewYork.com's Ohm Youngmisuk was used in this report.