City won their first ever Champions League trophy on Saturday shortly after conquering the Premier and the FA Cup.
The Citizens emulated United‘s legendary achievement from 1999, and it appears that left Williams feeling a little bitter.
The Red Devils’ left-back went on a strange rant on social media as he described City’s success as “sloppy seconds”.
Williams posted on Instagram: “Nobody wants sloppy seconds.”
The 22-year-old then criticised United legend Rio Ferdinand after the BT Sport pundit congratulated Jack Grealish and his City team-mates.
The full-back felt Ferdinand was wrong to praise the club’s rivals given his allegiances to the Old Trafford outfit.
Williams added: “@rioferdy5 Bet you don’t congratulate if you was [a] player. Keep the same morals. Two face are boring.”
According to ESPN, the club is disappointed with the ex-England youth international’s comments.
The Red Devils are also distancing themselves from the defender’s jibes as they are “not welcomed”.
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United have officially refused to directly comment on the matter.
Williams was restricted to just one appearance under manager Erik ten Hag this season and that took place at the Carabao Cup where he played only five minutes.
The academy graduate’s future is uncertain with his contract set to run out in 2024.
The former Norwich ace has registered a total of one goal and three assists in 51 appearances for the club ever since he was called up to the senior squad in 2019.