Zverev has won both their previous meetings. The last one was at Wimbledon in June and went to 5 sets. The other was on the clay in Hamburg in July 2014. Zverev won that one 7-5, 7-5.
Youzhny doesn’t have a great recent record at this tournament but seems to be enjoying playing in front of a home crowd this time. He beat Raonic in 3 sets in the last round. I expect him to have another strong match today and has a chance of taking at least a set.
Both their previous meetings were tight so the likelihood of 3 sets seems high. Lay Zverev if he breaks first. Remove the liability if Youzhny breaks back and holds.