The 33-year-old joined from Real Madrid for £70m in 2022 and has made 146 appearances.
He scored the opening goal in the 2023 Carabao Cup final win over Newcastle as Manchester United finished third in the Premier League in his first season.
But last year he was mentioned by new co-owner Sir Jim Ratcliffe who told BBC Sport some players were “not good enough” and “overpaid”.
The Brazil international said: “I will carry Manchester United with me throughout my entire life.
“It is not time to say goodbye; there are many more memories to create during the next four months.
“We still have a lot to fight for together; my complete focus will, as always, remain on giving my everything to help our club to succeed.”
While there has been external uncertainty over whether the club would trigger the additional year’s option in Casemiro’s contract, internally there was none.
Sir Jim Ratcliffe has publicly and privately highlighted the eye-watering £375,000-a-week wages paid to the Brazilian as an example of the profligacy that predated his arrival.
There was no way Ratcliffe would countenance extending that at a time when he is determined to cut costs and bring the wage bill down. Sources say the decision not to trigger the option was made some time ago, well in advance of Thursday’s announcement.
It is worth remembering Casemiro only came to United in 2022 because the club had failed to land Erik ten Hag’s top choices for the central midfield role he felt was essential to strengthen.
United missed out on Frenkie de Jong and Declan Rice, and after starting the season with successive defeats by Brighton and Brentford, where they lost 4-0 with Christian Eriksen and Fred in midfield, they completed the £70m deal with Real Madrid for Casemiro.
The reality is the Brazilian would not have moved unless United matched his wages and gave a four-year deal – and Ten Hag was adamant they could not go into the bulk of the season without someone of stature coming in.
That stance was justified initially as Casemiro’s performances in the first season were good as United finished third and reached the FA Cup final. It was the second campaign when the problems came. Casemiro’s form deserted him and the cost to bring him to the club began to look ridiculous.
After a 4-0 defeat at Crystal Palace in May 2024, Sky Sports pundit Jamie Carragher famously declared “leave football before football leaves you” about the former Real Madrid man. At the end of that season, when he was left out of Ten Hag’s FA Cup final starting line-up, Casemiro opted not to be involved at Wembley – and it seemed his time at United was over.
But his salary proved prohibitive and he stayed, eventually becoming an example to others of how a player can turn their situation around with hard work and commitment.
Former head coach Ruben Amorim repeatedly said at one stage Casemiro had dropped so far down in his thinking he was behind Toby Collyer – who is about to join Hull City on loan – in the pecking order.
Slowly though, the 33-year-old regained his form.
He started every game in the knockout phase, including the final, in last season’s Europa League campaign and has started 19 games out of a possible 20 in the Premier League this term, given he has missed two through suspension.
It is that form which brought debate about whether he should stay or not in the summer and, according to sources, it is to avoid that continuing speculation Casemiro asked for today’s announcement to be made.
Amorim previously said he had no doubts Casemiro would remain committed for the remainder of the season no matter what his contract situation was, and the player confirmed that in his statement.
However, he is now free to talk to potential suitors to sort out his future after this summer’s World Cup, for which he is expected to be in Brazil’s squad.
United, meanwhile, can move forward with their midfield transfer targets – Elliott Anderson, Carlos Baleba and Adam Wharton are high on that list – knowing their highest earner leaving gives them very useful financial flexibility.
