Rush said: "He is one of those full-backs that like to get forward and that will give the Reds' attack another option.
"With Finnan and Riise getting down the flanks, it will give opposing teams a lot to worry about.
"People will wonder what his arrival means for Jamie Carragher. For me, Jamie has been one of Liverpool's most consistent players for the last couple of seasons.
"It should not be forgotten, however, that he can also play very well at centre-back and will give Gerard Houllier another option there.
"Finnan is an international and has Premiership experience with Fulham. Coming to Liverpool is a big move for him and a lot is be expected from him."