Kasparaitis was injured in a knee-to-knee collision with Bruins defenseman Dan McGillis in the second period of Monday's 5-2 loss at Boston. An MRI on Tuesday revealed a tibial plateau fracture and a grade II MCL sprain.
"The doctor showed me the X-rays and I was shocked," said General Manager and Coach Glen Sather.
Losing Kasparaitis for the rest of the regular season is a major blow to the Rangers, who are trying to secure their first playoff berth since 1997.
New York will be without defenseman Greg de Vries at least two more weeks as he recovers from a sprained right knee, and defenseman Tom Poti missed Tuesday's finale of the home-and-home series with Boston because of a back injury.
Kasparaitis, 31, has one goal, nine assists, 48 penalty minutes and a solid plus-11 rating in 44 games this season.