According to the latest report from journalist Samuel Luckhurst, Manchester United are expected to activate the one-year extension option in Martinez's contract within the next four months.

Martinez's current contract has entered its final year, and with the extension clause, his deal can be extended until 2028 at the latest.
The club's senior management believes the renewal is almost certain to happen, but they hope the communication process can be better than the experiences of some former Manchester United players. Herrera, for example, only learned that his contract had been automatically extended after receiving a letter by mail at the time.
Martinez is currently 28 years old, and Manchester United are unlikely to simply allow him to leave as a free agent. However, the club needs to make a decision before next summer's transfer window arrives: whether to keep the player or sell him.