Borussia Dortmund are determined to keep hold of Erling Haaland amid pressure from Chelsea.
Sky Sports says Chelsea have been warned they are facing “mission impossible" as they step up their efforts to sign Haaland this summer.
Chelsea want to sign a No 9 during this window and Haaland is their top target.
He has a £70m release clause in his Dortmund contract which can be activated next summer. Clubs such as Chelsea, Manchester United and Real Madrid have been in talks to see whether they could buy him this summer at a premium price.
A source close to the discussions says Dortmund do not want to sell Haaland, especially because they are already letting Jadon Sancho join Manchester United this month in a £73m deal.