How much is a defender worth?

That question is posed by the £75m signing of Virgil van Dijk by Liverpool from Southampton. It is believed that he will be paid £180,000 a week.

Traditionally, it is strikers who have commanded the big transfer fees. To win matches you have to score goals. Moreover, in terms of attracting sponsors, a marquee signing of a striker gives a club a high profile.

However, to win matches you also have to avoid conceding too many goals and defensive fragility has been Liverpool's problem. One player won't solve that, but he will provide much needed leadership.

Southampton tend to end up selling their best players, usually at a good profit. That gives the club financial stability, even if it puts paid to any hopes of pushing on to the next level. The risk for a solid mid-table club is getting sucked into a relegation battle, and it is a risk that the Saints face at the moment.

The price of defenders has been going up over time. In 1998 Jap Stam commanded £10.6m when he went from PSV to Manchester United. Rio Ferdinand cost £18m when he went from West Ham to Leeds and £12m more when he was transferred to Manchester United two years later.

By 2014 David Luiz could fetch £50m when he moved from Chelsea to PSG. Three years later Kyle Walker cost £54m when he moved from Tottenham to Manchester City. The sale of van Dijk represents a 39 per cent increase on that figure.

His transfer has brought a windfall for Celtic who were canny enough to include a 10 per cent sell on clause when he moved to Southampton. The £7m they will receive is more than double the prize money awarded to them for winning the Scottish championship last season which says something about the financial state of Scottish football: Celtic windfall