For the sake of competition and change Youzhny in 3.
However Youzhny's fatigue will be even more fundamental to tomorrow's match than Federer's level.
If Youzhny can withstand fatigue he can give Federer a very tough match tommorow, otherwise Federer could only face one tough set, or maybe none at all.
Well Youzhny will certainly feel some fatigue. He has been on a roll for a while. It is also mentally tiring to focus so much on several big matches.
However, Federer has been off competitive tennis for a month. He has only played 3 matches since Australia.
So Youzhny's fatigue may not be instrumental. It will be a combination of fatigue versus rustiness that will determine the winner. And not to mention 8-0 h2h.