In an interview with SPORT1, Rolfes said: "Yes I'm sure [he will stay]. One [reason] is contract constellations. The other thing is how comfortable he feels, the family, himself and that he knows what he has in the club. Also that he has a very good team, we will have a very good perspective next year and there is no change in the team.
"We will definitely have a top team available next year. These are all points that, in addition to contracts, coaches like Xabi but also players who arouse interest from other clubs often keep us with us."
He added: "He surprises me every now and then. What we and he always say internally: Everyone has their role and we have a good squad. Everyone has the quality to play a good role. Xabi has the courage to not only commit to an eleven but also to say: I'll adapt the system and bring other guys onto the pitch. We are not trapped in the system that is based on how we play football."