The Barclays Premier League club have yet to confirm the news but Jack Sullivan - son of Hammers' joint-chairman David Sullivan - tweeted on Wednesday evening that the defender sustained the problem in training and faces up to six weeks on the sidelines.
Sullivan wrote: "Very bad news..
Reid Injured in training 4-6 weeks with hamstring
But some players will return faster than anticipated due to hard work."
If New Zealand international Reid is indeed injured, he will join a growing list at Upton Park, with midfielder Manuel Lanzini ruled out for six weeks with a thigh injury and Diafra Sakho out for three months with a thigh problem of his own.
Victor Moses is still sweating on the results of a scan on his hamstring, while Dimitri Payet is out until February and Enner Valencia has been missing since suffering a knee injury in July, although he is closing in on a return.
Source : PA
Source: PA