Bojan, 30, played for Stoke between 2014 and 2019 after beginning his career at Barcelona.
He has been without a team since leaving Major League Soccer side Montreal Impact at the end of 2020.
"This opportunity is one of the best, both personally and professionally, and I can't wait for this big challenge," said Bojan.
"Iniesta is special to me and I am happy to be able to play with him again. I want to score a lot of goals from his assistance."
He made one international appearance for Spain and scored 16 times in 86 games, including 14 Premier League goals, during his five-year spell at Stoke.
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