Van der Vaart lasted just 12 minutes of Sunday's 2-1 win at White Hart Lane before being replaced by Jermain Defoe.
"Rafa felt it tear, so that doesn't look too good," said Redknapp.
"Younes felt he might have torn a muscle in his hip. He felt that go.
"It's so disappointing for Rafa. He keeps picking up little injuries.
"It's probably because he's missed a pre-season or was away at the World Cup and not played many games.
"When your fitness is a bit low it's hard to get up to speed. He keeps getting little nicks."