Shumpert suffered the injury in the third quarter of the Knicks-Celtics game on Sunday and did not return.
"I've never had it before. It's pretty numb," Shumpert said after the Knicks' 106-104 win.
Shumpert's right knee buckled during a collision with Boston's Chris Wilcox. He walked off the floor gingerly and was then helped off of the bench by two Knicks staffers.
"I really don't know how it happened," Shumpert said. "I just remember being in the lane, shot going up, somebody fell into my knee. I think the initial scare was worse than it might be."
Shumpert, the Knicks' first-round draft pick, had 11 points on 3-of-13 shooting and four rebounds in 22 minutes.
Knicks coach Mike D'Antoni downplayed the significance of losing Shumpert. He believes Bibby will return shortly and fill in behind Douglas.
But two weeks off in a truncated 66-game season will certainly hurt the rookie's development.
"I've just got to be tough mentally," Shumpert said. "Those guys were telling me it's a long season, you're going to hit bumps in the road. But I thought they were talking about some different bumps. I've got to get through it."
Also, reserve forward/center Jared Jeffries left the game midway through the third quarter with a calf injury. Jeffries became entangled with Boston's Jermaine O'Neal on a lay-up attempt. He is expected to be out 1-2 weeks, according to the team.
Jeffries appeared to aggravate a previous right calf injury that held him out of the Knicks' preseason finale on Wednesday.
Ian Begley is a regular contributor to ESPNNewYork.com.