Willian is set to leave Chelsea on a free transfer after seven seasons with the club.
The 32-year-old is linked with a move to Arsenal.
“The time has now come to move on. I am certainly going to miss my team-mates. I will miss all the staff at the club who’ve always treated me like a son and I will miss the fans.
“I leave with my head held high, safe in the knowledge that I won things here and always did my best in a Chelsea shirt. My heartfelt thanks go out to all of you and God bless you," wrote Willian in an open letter on Twitter.
Willian scored 63 goals in 339 total appearances with the club.