Adrian Clarke analyses the tactical impact Premier League summer signings will have on their clubs.
Issa Diop could be the man to do just that.
Although they finished 13th in the Premier League last season, West Ham endured their worst defensive return since they let in 70 goals and finished bottom in 2010/11.
No PL team conceded more than the Hammers' 68 in 2017/18.
Pellegrini's response was to break the club's transfer record to bring in one of European football’s most promising young defenders.
Signed from Toulouse, Diop is an intimidating presence who stands at 193cm.
Pellegrini must hope he can use the Frenchman's imposing frame to improve one of his side's main weaknesses.
West Ham conceded 16 goals from set-pieces last season, the third-most in the league.
When defending corners and free-kicks last season West Ham missed the presence of the injured Winston Reid, whose absence has been extended for a further three months after a setback.
Their most successful defender in the air was Angelo Ogbonna, but the 80 aerial duels he won ranked him joint-50th in the league.
Diop has a better success rate in the air than most of West Ham's defenders so should make it harder for opponents to attack high balls.
|2017/18||Aerial success||Aerials won||PL rank|
Diop is strong and uses his pace to cover his team-mates with recovery sprints.
West Ham's backline lacked speed last term so the 21-year-old's addition should allow Pellegrini's side to hold a higher line and press from the front.
Pressing was not something West Ham did much of last season. They ranked 15th in the PL for the number of times possession was won in the final third.
Diop has also made a name for himself as a reliable ball winner. He made 58 tackles last season and his 76 interceptions were the fifth most in France's top flight.
While he has primarily been signed to improve the defence, Diop also offers an attacking threat.
The France Under-21 international scored three league goals in 2017/18. No West Ham centre-back managed more than one last season.
Diop is also confident in possession. He averaged 17 forward passes per 90 minutes last season, many of which were short, intricate and between the lines.
Nearly 18 per cent of West Ham's passes last term were classified as "long", so Pellegrini may use Diop to shorten up their distribution.
He may be young but with 85 Ligue 1 appearances behind him across the last three seasons Diop is ready to make his mark.
I expect him to be a key man for West Ham.