Mainz chief Christian Heidel is convinced the Bundesliga title will be fought by Borussia Dortmund and Bayern Munich.
"Dortmund and Bayern have the title for themselves this season", Heidel, who is friends with former Mainz coach Klopp, told Bild.
"After the Champions League performance they put in this week, I think Dortmund are actually one step further ahead than Bayern. They always buy top players. Their squad is really strong.
"However, we want to annoy Dortmund for as long as possible. We'll try everything to win."