Despite apparent interest from Everton, Sunderland must not sell star centre-back Lamine Kone.
Everton's need for a centre back has intensified following the departure of John Stones to Manchester City, and they are also expected to complete a move for Wales and Swansea captain Ashley Williams.
Despite the potential profit that the Black Cats could make on Kone, who Sam Allardyce signed for £5 million, Sunderland simply cannot afford to sell their man.
It has been a summer of turmoil on Wearside, which has seen the departure of Allardyce and only one incoming player, Papy Djilobodji from Chelsea.
The last thing Sunderland need before the season starts is to lose one of their key players, especially with how thin their squad already is.
From a business standpoint, the club may be inclined to let Kone go for triple the money they signed him for, but they could pay an even greater price if they lose their Premier League status next May.
Kone was a revelation for Sunderland when he arrived last January, and with the money being spent on players this summer, there isn't much of a chance of being able to find someone of the same quality for a minimal fee.
Sunderland supporters have had a frustrating summer with the lack of activity, and the departure of a fan-favourite would surely create more panic for a fan-base who are still longing for a period of calm at the club.
As tempting as the money being offered for Kone is, the decision to keep him will pay for itself if his performances over the season ensure that David Moyes keeps Sunderland in the top tier of English football.
It may seem foolish to discuss relegation before the season has even begun, but that is how pivotal a player like Kone can be to Sunderland. The Black Cats need a solid base at the back just as much as they need Jermain Defoe's goals up top.
£18 million may be considered a lot of money for man that they spent £5 million on just over six months ago, but if Sunderland are to progress and have a period of stability, they cannot afford to sell their top players to divisional rivals and put their own position in jeopardy.
If the ambition of Sunderland is to continue to be a Premier League club and steer away from constant relegation battles, selling their biggest assets is not the way to go about that.
Kone is one of their biggest assets, and must stay at the Stadium of Light.