The London club parted ways with the Australian on Friday, ending a turbulent spell that saw the club finish 17th in the Premier League despite winning the Europa League.
While the European success appeared to boost his chances of staying, the club ultimately decided his league results weren’t acceptable and chose to move on.
"Gaffer, where to start,” Maddison wrote on X.
"Firstly, thank you for bringing me to this wonderful club that I now call my home. Your instant belief in me to not only sign me but make me the clubs vice captain & part of the leadership group from the get go is something I’ll always be thankful for.
"Secondly for the Europa League campaign that started in our stadium on gameweek one and finished perfectly with that special night in Bilbao. You led us to victory and we’re European champions and in this clubs history books because of you and your winning mentality.
"Lastly and most importantly is how you are as a man and a person. Your unwavering self belief and strong mindset is infectious and a massive reason in why you were the man to end this clubs 17 year drought for a trophy. A family man with great morals & I have honestly learnt so much from you. More than you will probably ever know. All the very best. Madders."