Sandro Tonali's contract has been extended until 2029, with the option of an additional year.
The Italian agreed the deal in secret during his ban for illegal betting, to protect Newcastle financially, with the club having not been able to use him for 10 months.
Tonali now has three and a half years left on his deal, with the option of one more.
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Highlights from the Premier League match between Brighton and Newcastle.
The previous contract he signed when he joined the club from AC Milan in July 2023 had been due to expire in the summer of 2028.
The Italy international played 45 times in all competitions last term, after he returned from the aforementioned ban, scoring six goals and providing three assists.
He has started all eight of Newcastle's Premier League games so far in 2025/26.