Koeman said: "He is a player with experience and would offer some options for our game."
Valencia sporting director Miguel Angel Ruiz said: "We want to improve our squad."
Valencia have already crashed out of the Champions League and are determined to send a strong message to their fans.
The Spaniards first approach for European Cup winner Riise was rejected. They are set to go back for him, though Benitez is determined to fend them off.
Norway international defender Riise is a regular at Anfield and can play at left-back or in left midfield.