"I have a year left on my Sunderland contract and would gladly go back," Haas told the Football Association's official website.
"I only came to Switzerland because Peter Reid made it clear he didn't want me. I've been in Swiss football for seven years and want the new challenge.
"That is why I went to the Premiership in the first place, and what happened to me hasn't put me off at all.
"The Sunderland players tell me the new manager Howard Wilkinson has made a lot of changes and it's been very good."
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