Sauber are edging closer to sixth-placed Force India in the constructors' championship standings by snatching 38 points from their last four races.
"Sauber have been doing a very good job lately," ESPN quotes Mallya as saying.
"They are the in-form team at the moment and they have been taking all the opportunities that were presented to them.
"It's going to be a real fight in these last four races. We need to make a step forward to hold them off, because they can qualify well and they have strong race pace as well."
Force India have scored just three points from their last seven races.