The Nigeria international spent the 2025-26 season with the Scottish champions, helping Celtic secure a domestic double by winning the Scottish Premiership and Scottish Cup.
Iheanacho scored nine goals across all competitions during his only campaign at Parkhead, delivering several important contributions along the way.
He thanked Celtic, his teammates, coaches and supporters for making his time in Glasgow a memorable experience.
“To the Celtic FC, what we achieved last season was truly incredible, I’ll forever be grateful for the opportunity to represent your great football club,” Iheanacho wrote on Instagram.
“My thanks to Brendan Rodgers for bringing me to the football club. Thank you to Martin O’Neil and his staff. Special thanks to my teammates, will miss you guys.
“To the amazing fans, thank you for your unwavering support. I wish you all the very best for the upcoming season and beyond.”