Granit Xhaka is a key figure for Bayer Leverkusen and the Bundesliga side cannot afford to let the Swiss midfielder leave, manager Erik ten Hag said amid reports linking him to a move to Sunderland.
Leverkusen have already lost playmaker Florian Wirtz and defender Jeremie Frimpong to Premier League champions Liverpool, while centre back Jonathan Tah has moved to Bayern Munich.
Former Arsenal man Xhaka has been linked with a move to Sunderland, with his agent telling German media the 32-year-old Switzerland skipper has an agreement in principle with the newly promoted Premier League club.
"The agent can say anything. But this club has already lost three important players," Ten Hag told German media on Tuesday.
"We won't let any more players go, that's not possible. That would neglect the structure and also the culture of the squad.
"It's clear, Granit is a leader; he has signed here for five years and has three years left on his contract. He's too important for us to let him go."
Xhaka helped Leverkusen secure the double in the 2023-24 season as they lifted their first Bundesliga title without losing a game, won the German Cup and reached the Europa League final.
He has made 99 appearances for Leverkusen, scoring six goals and registering nine assists.
Former Manchester United manager Ten Hag replaced Xabi Alonso in May after the Spaniard left to manage his former club, Real Madrid.