Mainz are currently seventh in the standings on 17 points, just three adrift of third-placed Eintracht Frankfurt and three above Hamburg in 10th.
An impressed Fink said: "Mainz are tough opponents who are in good form at the moment.
"What sets them apart is the way they play their own game without any fear, attacking well and with a good blend in their side too.
"We have got to watch out, but we are capable of beating them at home in any case."
The chances of a home victory have been hit by the loss of defender Paul Scharner to suspension, but Michael Mancienne is back after illness and he or Jeffrey Bruma will step in to fill the void at the heart of the defence.
"I will wait and see what impressions I get from our final training session," said Fink of his selection plans at his pre-match press conference.
The only impression Mainz coach Thomas Tuchel gets of his side is one which is improving.
"The team have gelled more compared to a year ago," said Tuchel, whose side have picked up 13 points from their last six games.
"We now have a team spirit which is second to none.
"This is a good phase for us."
Fortunately for both Tuchel and Fink, none of their players have come back from international duty with any injuries, although tiredness could have an influence.
"Poor Elkin (Soto) practically had to get off the plane from America and straight into the plane taking us to Hamburg," said Tuchel of his Colombia midfielder.