Chelsea currently remain at a stalemate with Rudiger regarding a possible contract extension. The former Roma man could walk away for free at the end of the season and seek a lucrative deal elsewhere, but Keown has stressed his importance to the side.
"He's a real driving force for Chelsea – I love watching him play," Keown told BBC's Match of the Day.
"I was an aggressive defender myself, but I think this guy takes it to another level.
"When he gets the ball, he likes to run forward. The fans love him there because he makes things happen.
"Defensively – he's so aggressive. He just shuts the door. So aggressive, strong, and he really leads from the back.
"He's a nuisance to play against and he's been outstanding for them."
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