The Austrian-born centre-half, 31, who had a year left on his deal at Oakwell, was keen to return to Europe to be closer to his young family and has now been allowed to leave for the continent.
Sollbauer was widely viewed as a catalyst for the Reds’ ‘Great Escape’ in the second half of the 2019-20 campaign after being brought in by former head coach Gerhard Struber from old club Wolfsberger AC in January, 2020.
Sollbauer made 18 starts in all competitions following his arrival at Oakwell and featured 43 times in Barnsley’s Championship play-off season in 2020-21.
But he found his starting opportunities more restricted from January onwards with Toby Sibbick often preferred in the starting line-up by ex-head coach Valerien Ismael in the second half of the year.
Commenting on the departure, co-chairman, Paul Conway said: "The board of directors at Barnsley Football Club would like to thank Michael for his incredible service to the club for the last two seasons. Michael provided incredible commitment to the club and set a great example of professionalism for the entire squad.
“When Michael asked to be able to return to Europe to reunite with his family, we absolutely had to reciprocate his professionalism and allow this move. We will all be following Sole in his new journey and wish him and his family the best."