The guard tore the anterior cruciate ligament in her right knee Friday night during New York's 75-69 loss to the Detroit Shock before 11,110 at Madison Square Garden.
It was the eighth consecutive victory for the Eastern Conference-leading Shock (8-1), which defeated the Liberty for the second time in a week. Deanna Nolan led the Shock with 20 points.
Elena Baranova, acquired in the dispersal draft, led New York with her season highs of 20 points and 10 rebounds. The Liberty (6-5) didn't learn of the extent of Hammon's injury until after the game.
"This is an incredibly bad break for a person who is having an All-Star year and who worked so hard in the off-season to become one of the team's best players," Liberty Coach Richie Adubato said.
Hammon, averaging 16.2 points a game, was injured only 12 seconds after entering the game with 14:55 left in the first half. She quickly grabbed a rebound, started upcourt, stopped and planted her right foot at the Liberty's three-point line, then fell to the floor clutching her right knee.
Seattle 71, Cleveland 59 -- Lauren Jackson scored 16 points and Sue Bird added 11 points and 12 assists as the Storm (7-5) beat the Rockers (5-6) before 6,065 at Cleveland. Jackson, the WNBA's leading scorer at 19.4 points a game, was held scoreless in the second half, but it didn't matter.
Cleveland made 11 of its 17 turnovers in the first half and fell behind, 39-29.
Minnesota 67, Phoenix 59 -- Katie Smith made four three-point shots and finished with 18 points as the Lynx (6-6) beat the Mercury (2-11) before 6,237 at Minneapolis. Tamicha Jackson led the Mercury with 18 points.