City became just the second English team to ever win the triple crown on Saturday after defeating Inter Milan 1-0 in the Champions League final.
Zinchenko left City at the beginning of the season after enjoying much success there. He then moved on to a new challenge.
The Premier League title battle saw his new team compete head-to-head with the defending champions before falling short, leaving Arsenal fans heartbroken and still hoping for their first championship since 2004.
Zinchenko infuriated online Arsenal supporters when he shared City's post celebrating winning the Champions League along with three clapping emojis.
One irate Twitter user shared Zinchenko's tweet and said, "Nah, sell this guy as soon as possible."
Another admirer chimed in, "This is pure nonsense from Zinchenko!" while a third declared, "Zinchenko is pathetic."
Before leaving City last summer, the Ukrainian played for the club for seven years and well over 100 times.
He was a £30 million investment for Arsenal, and he frequently displayed his emotions on the field of play, especially following a setback.
While some Gunners followers may not agree with the 26-year-old, others did recognize the message of congrats.
One supporter remarked, "I don't see anything wrong with what Zinchenko posted." That's good sportsmanship. We'll try again the following year, perhaps with all of our tools finished, and we can then enjoy the congratulations of others.
Zinchenko can't thank his former teammates because he plays for Arsenal, right? one more said. "Hear how stupid you sound when you listen to yourself."
After becoming the first team to win the triple crown since 1999, Zinchenko's old teammates partied late into the night in Istanbul.
In a physical contest, Rodri's goal in the second half was sufficient for Pep Guardiola's team to win the Champions League for the first time ever.
Zinchenko sends a congrats message to Man City, leaving Arsenal fans fuming.
Oleksandr Zinchenko has angered Arsenal supporters after the defender thanked Manchester City on Instagram.