Willian has announced the "time has now come" to leave Chelsea amid repeated reports of a free transfer switch to London rivals Arsenal.
The Brazil forward, who turned 32 on Sunday, is out of contract following a seven-year stay at Stamford Bridge.
Willian won two Premier League titles, an FA Cup, a League Cup and the Europa League with the Blues and said he would depart with his "head held high".
"The time has now come to move on. I am certainly going to miss my team-mates," he wrote in an open letter to Blues fans published on Twitter.
"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."
Willian, who has been struggling with an ankle injury, missed last weekend's FA Cup final loss to the Gunners, as well as Saturday's Champions League exit at Bayern Munich.
Having turned down Tottenham to join Chelsea from Russian club Anzhi Makhachkala in 2013, he scored 63 goals in 339 appearances.
If reports are to be believed, he could remain in the capital, playing under Mikel Arteta at the Emirates Stadium.
"They were seven wonderful years. In August 2013 when I received the offer from Chelsea, I was convinced that this was where I had to play," he wrote, reflecting on his time with the Blues.
"Today I am certain that it was the best of decisions. There were so many happy times, some sad, there were trophies and it was always very intense.
"There was also criticism, which is normal, what is important though is that both the affection and criticism drove me to always give my all in every training session, every game, to be constantly improving until my very last minute in a Chelsea shirt."
Ahead of Saturday's 4-1 European mauling in Munich, which completed a 7-1 aggregate loss, Chelsea boss Frank Lampard said there would be no hard feelings if Willian opted to leave.
Another player heading for the exit door is fellow forward Pedro.
The Spaniard, who suffered a shoulder injury in the FA Cup final, is set to join Roma on a free transfer and bid a fond farewell to his current employers.
"After five wonderful years my stage at Chelsea FC comes to an end," he wrote on Instagram.
"It's been a pleasure and an honour to play for this club and win the Premier League, FA Cup and Europa League titles, as well as competing in one of the world's best football leagues. I made the right choice, I take with me wonderful and unforgettable memories.
"I say farewell very pleased with this stage of my career, and I'm also very excited with the next to begin. Thanks and good luck for the future."
After securing Champions League qualification through a fourth-placed finish, Lampard's first campaign as boss ended on disappointing notes with the cup final loss followed by a difficult trip to Germany.
Nevertheless, Tammy Abraham, who claimed his side's consolation at the Allianz Arena, hailed a "phenomenal" season for the club and believes his maiden year in the Premier League could not have gone much better.
The England striker registered 18 goals in all competitions during his breakthrough campaign in west London – an achievement he is eager to build on.
"It's been a phenomenal season for myself and the lads," the 22-year-old told Chelsea TV.
"I couldn't have asked for a better season. I have had a few niggles here and there, but I have come out stronger and now I have to build myself for next season and start well and end well. That's my aim. I have to raise my bar and go again."
