In the Hammers' quest to bolster at the back, the Manchester United centre-back had emerged as a top target but Maguire will now remain at Old Trafford.
Back to the drawing board, then, for the Hammers, and WhoScored.com have picked out four they believe West Ham can target in the coming days.
Konstantinos Mavropanos (VfB Stuttgart)
With Wataru Endo set to leave VfB Stuttgart, the German side will be keen to avoid losing two key men before the month is out.
Greek man-mountain Konstantinos Mavropanos has emerged as a top centre-back target for the Hammers as they look to quickly secure the services of a Harry Maguire alternative.
The 25-year-old has a knack for being in the right place at the right time to alleviate pressure on his side's goal.
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Indeed, Mavropanos ranked 22nd for clearances (97) in the Bundesliga last season.
The Greek centre-back stands at 6ft 4in, and he maximises his height to dominate in the air. Of the 149 players to contest at least 50 aerial duels, only Dan-Axel Zagadou (72.6 per cent) had a better aerial success rate than Mavropanos (70.4 per cent) in the Bundesliga last season.
Factor in that he ranked ninth for tackles and interceptions combined (113) and it's easy to see why West Ham are prioritising Mavropanos.
Jonathan Tah (Bayer Leverkusen)
However, should VfB Stuttgart steadfastly refuse to cash in on Mavropanos, then West Ham need to have contingencies, and one of those should be Jonathan Tah.
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The German has routinely been linked with a Premier League switch, though any move to England have never come to fruition.
Should the Hammers fail in a move for Mavropanos, Tah could be a viable option for David Moyes' side.
Like Mavropanos, the 27-year-old Bayer Leverkusen man is one who knows how to clear the decks.
On hand when needed he ranked 15th for clearances (117) in the 2022/23 Bundesliga campaign.
In addition, Tah is a more accomplished centre-back when on the ball have returned the 12th best pass success rate (89.1 per cent) in Germany's top tier last term, that an improvement on Mavropanos (83.5 per cent).
The latter should be the priority, but the former wouldn't be a poor pick up as West Ham seek a new centre-back.
Jean-Clair Todibo (Nice)
Harry Maguire's decision to remain at Manchester United impacts their own pursuit of a new centre-back.
The Red Devils had been linked with a move for Jean-Clair Todibo when it was expected that Maguire would leave, but the Frenchman is unlikely to secure a move to Manchester this month now.
Could a switch to London be on the cards instead? Todibo was a rumoured target for West Ham earlier this summer, and he made a bright start to 2023/24 in Nice's 1-1 draw with Lille in the Ligue 1 season opener last week.
The 23-year-old has won possession in the defensive third more times (182) than any other player since the start of the 2022/23 Ligue 1 campaign.
And he is an accomplished distributor too having ranked 11th for accurate passes (1975) over the same period.
Todibo also places 19th for clearances (109) so another proactive centre-back that would certainly aid the Hammers.
Nice would demand a hefty fee for the Frenchman, but the financial windfall from Rice's departure, even with the signings of Edson Alvarez and James Ward-Prowse, means the east London side could afford Todibo.
Luiz Felipe (Real Betis)
West Ham were linked with walking red card Luiz Felipe earlier this summer, only for the links to cool as they prioritised Harry Maguire.
However, the Hammers may yet turn back to the Italy international as they seek to bolster their backline.
The 26-year-old was sent off three times in LaLiga last season, and received his marching orders for headbutting Burnley's Johan Berg Gudmundsson in a pre-season friendly last month.
Sort the disciplinary issues, though, and Felipe would be a solid addition to the West Ham defence.
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He ranks 21st for clearances (105) since the start of the 2022/23 LaLiga season, this despite starting just 23 of a possible 39 matches in that time, so knows when to get the ball away from danger.
The cons, though, outweigh the pros. Felipe should be low on the priorities list for West Ham, who would be better investing in a centre-back who isn't prone to moments of madness.