"Rafael has torn a hamstring, so that does not look too good.
"He's going to be out. He'll have a scan," said Redknapp, who also saw defender Younes Kaboul have to go off with a hip problem.
Van der Vaart has been in inspirational form since his £8m deadline-day move to White Hart Lane from Real Madrid, scoring eight goals in 14 appearances, has picked up a number of minor injuries.
He missed Tottenham's previous match against Werder Bremen with an ankle knock and
was hindered by a niggling hamstring strain earlier in November.
"He keeps picking up injuries, little injuries. He's a fantastic footballer and he's important to us, we need him," Redknapp added.
Big three points, great week
mightyspurs765
There may be compensation for Spurs if Kaboul is sidelined, with Michael Dawson almost ready to return.
Redknapp revealed that the England international will play in a reserve or friendly match on Tuesday after taking longer than
initially expected to recover from spraining knee ligaments against Bulgaria in September.
Sunday's victory over Liverpool, the third consecutive season Spurs have won the fixture 2-1, moved Redknapp's side up to fifth in the table.
It was also the fifth time this season that Redknapp's side have taken all three points in the league after initially falling behind and extends their winning streak to four matches.
"It was a great performance to come from one down," stated Redkanpp.
"When we missed the penalty I've got to be honest, I thought maybe it wasn't going to be our day. But we kept going.
"Even if you're one down, we're always going to make plenty of opportunities and it's a case of sticking them away."
Source: BBC Sport
Source: BBC Sport