Kewell is on the road to recovery, having played 25 minutes for the reserves last week. He is also expected to play a part in Australia's international friendly with Jamaica this weekend.
"We are waiting for Harry because he can be an important player for us. Having him fit again will improve our squad," said Benitez.
"Every day he is feeling a bit better. He's away with Australia this weekend and then we'll have to see if he can be involved against Blackburn. It may be too soon but we'll have to wait and see.
"When he's back with us it'll be like signing a new player because he has a lot of quality. He is a different kind of player to what we have. He can beat people, cross balls into the area, shoot and also score goals himself. He has been out a long time so he will be hungry to get back.
"He will bring ability, experience and energy to our team and I'm looking forward to having him available again."