The midfielder departs Oakwell for Belgian side K.A.S Eupen for an undisclosed fee.
Joining the Reds from Liverpool in September 2020, Isaac made two first-team appearances for Barnsley towards the back end of the 2021/22 season.
Isaac had the following to say:
"I would like to say thank you for the support from the fans, all the staff and every teammate for my time at Barnsley. I hope the club will bounce back to where they belong.
"Good luck for the season".
We would like to thank Isaac for his professionalism and hard work during his time at Oakwell.