It’s a major blow for the Hammers, what with the New Zealand international being at the very top of his game this season and undoubtedly the club’s best performing centre-back.
West Ham are currently in the midst of an injury crisis, and Reid’s absence leaves them short on options with centre-back James Tomkins currently playing at right-back in place of Carl Jenkinson.
With Tomkins becoming an increasingly important player at Upton Park, it almost certainly rules out the prospect of him moving to Sunderland in the upcoming January transfer window.
And Reid’s injury could scupper another one of Sunderland’s transfer plans as reported target James Collins is now largely expected to feature more in Reid's absence.
According to a recent report in the Mirror, Sunderland were said to plotting deals to bring both Tomkins and Collins to the Stadium of Light in January.
Tomkins was always going to be a little farfetched, yet Collins was a very realistic possibility as the Welsh international enters the final six months of his contract and finds himself out of favour in East London.
With Wales qualifying for the European Championships, Collins has spoken in length of the importance of playing regularly in order to boost his chances of selection in France next summer.
The 32-year-old has made just three Premier League appearances this season, and with Sam Allardyce also being a leading factor, a Sunderland switch ultimately made a lot of sense.
But now Reid’s injury is likely to hinder the possibility of a switch as Collins could find himself back in first-team contention at least up until the end of January, starting with the visit of Stoke City this weekend.