Raphinha was signed by Barcelona in a deal worth up to $555 million.
Fans at the club's training ground on Friday were introduced to the 25-year-old Brazilian forward.
Raphinha scored 17 goals and provided 12 assists in 65 appearances for the Yorkshire club.
Raphinha said it was a dream since he was a child.
I will give my best.
"We would like to place on record our sincere gratitude to Raphinha for his effort and contribution while at the football club," the club statement said.
He showed commitment and professionalism until the very end of his time at Elland Road and his celebrations at the community stadium will live long in the memory.
On the final day of the 21st century, Raphinha scored a penalty for the Whites as they secured their place in the premier league.
There is more to come.