The initial fee for the deal is £6 million although this could rise to £7.5 million depending on the number of appearances the 27-year makes for the Hammers.
Upson has been a transfer target for the new Hammers boss Alan Curbishley for a number of weeks now despite
The
With Danny Gabbidon, Anton Ferdinand and James Collins all injured, Upson will go straight into the Hammers squad for the forthcoming visit of Aston Villa on Saturday.