Sporting Lisbon coach Ruben Amorim says his future "hasn't been decided yet" amid interest from Manchester United.

"Nobody knows if this was my farewell match, or if there will be a farewell match," Amorim said in quotes reported by Portugal's sports daily A Bola after Sporting's 3-1 win over Nacional in the Portuguese League Cup quarter-finals.

Hours earlier, Sporting released a statement to the Lisbon Stock Exchange, saying they have told United that Amorim has a release clause worth 10 million euros ($A16 million) in his contract.

The Portuguese champions said United "has shown interest" in paying that amount.

United are looking to replace Erik ten Hag, who was fired on Monday with the team languishing in 14th place in the Premier League.

Ten Hag was the 20-time English champions' fifth permanent manager since Sir Alex Ferguson retired in 2013. United haven't won the league since Ferguson's departure.

The 39-year-old Amorim has coached Sporting since 2020, leading the team to Portuguese league titles in 2021 and last season.

Sporting lead the league this season, too, having won all nine of their games, bolstering Amorim's reputation as one of Europe's most talented coaches.

He reportedly held talks with West Ham United last season and was linked with replacing Juergen Klopp at Liverpool before Arne Slot was hired.

Amorim is a former Portugal midfielder who spent the majority of his club career at Benfica.

His contract at Sporting expires in 2026.

Manchester City manager Pep Guardiola was asked earlier on Tuesday if he thought Amorim has what it takes to succeed in the Premier League.

"All I can talk about is the experience of playing twice against Ruben's Sporting Lisbon team (in the Champions League in 2022), and the pressure was really, really good," Guardiola said.

"I spoke with (current City player) Matheus Nunes, and he was his player, and he speaks highly about him. And look this season, he is unbeaten and winning all the games in the Portuguese league and (in) the Champions League, (they have) the same points as us. So a high manager. I have the feeling that Man United, what I hear, that they are thinking about him, it's because he's a good manager."

Ruud van Nistelrooy will take interim control of the team for United's English League Cup match against Leicester City at Old Trafford on Thursday (AEDT).

With AP.