Manchester United have been crying out for a world-class central defender in the last few years.
This has only been amplified by Liverpool's capture of Virgil van Dijk, which has improved United's rivals immensely, as they finished second in the Premier League and became champions of Europe, with the Dutchman playing a key role.
But, if United could pull off the signing of Kalidou Koulibaly from Napoli, the hope is that he could make just as much of an impact as Van Dijk has for Liverpool.
He's not likely to be cheap, but he would be a significant upgrade on their current defensive options.
So, just how much would the signing of Koulibaly improve United's performance?
We used Football Manager 2019 to find out.
Kalidou Koulibaly - Napoli
Current overall ability: 168/200
Potential overall ability: 171/200
Best attributes (out of 20): Strength (19), balance (19), marking (18), tackling (17), pace (17), stamina (17), heading (16), work rate (16), positioning (16), determination (16), bravery (16), anticipation (16).
Koulibaly's profile on Football Manager 2019 highlights just how good a defender he is, with incredibly high ratings in all defensive attributes, whilst also being physically powerful, quick across the ground and technically proficient.
To find out how Koulibaly's arrival would impact United's performance in 2019/20, we added in a future transfer of £95 million from Napoli, along with Daniel James from Swansea and included all other transfers from around the world, using a fan-made editor file.
But how much difference will he make to United's performance in the 2019/20 season?
Here's what happened....
Manchester United 2019/20 transfers - according to the game
Transfers in: £171 million
Kalidou Koulibaly (Napoli) - £95 million
Iago Aspas (Celta Vigo) - £36 million
Luka Milivojevic (Crystal Palace) - £22 million rising to £24 million
Ever Banega (Sevilla) - £18 million
Transfers out: £1 million
Lee Grant (Orlando City) - £1 million
So how did this affect their season?
Manchester United Premier League goals conceded in 2018/19: 54
Manchester United Premier League goals conceded in 2019/20: 31
After Koulibaly's big money arrival, United conceded 23 less goals than they did last season, despite not signing another defender in the window. That's money well spent.
Manchester United Premier League clean sheets in 2018/19: 7
Manchester United Premier League clean sheets in 2019/20: 16
United also managed to more than double their clean sheet record, with 16 in total for the season. Shows what a world class defender can bring.
Kalidou Koulibaly's 2019/20 season for Manchester United
The Senegalese international had an outstanding individual season for United, making 52 appearances in all competitions, scoring three goals, registering two assists and an average rating of 7.27 overall.
Manchester United's 2018/19 league position: 6th
Manchester United's 2019/20 league position: 5th
However, despite their defensive improvements, United would miss out on the top four again in 2019/20, just one point behind Tottenham. That's despite scoring more goals and conceding less than Spurs. It just shows how tight the Premier League could be next season.
Manchester United's best XI in 2019/20
This is the 11 that Ole Gunnar Solskjaer used most often in 2019/20 according to the game, which looks much stronger than last season.
Victor Lindelof partnered Koulibaly in central defence, with Milivojevic, Pogba and Matic forming a midfield three. Dalot broke through and made the right back spot his own, with Martial, Rashford and Mata making up the front three.
Football Manager 2019 suggests that if Manchester United can sign Koulibaly this summer, he will improve their defensive record considerably, but unless Solskjaer can bring in more quality to other areas, the top four might be out of reach again.
United have started the summer transfer window well, but more additions are needed.
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