The signing from Leeds United has apparently pushed them over their limit.
The deal, which was for an undisclosed fee, was finalised yesterday after days of speculation.
The 22-year-old, who also had an offer on the table from Everton, was out of contract at Elland Road this summer which saw the Championship club open to selling one of their prized assets.
However the bargain deal may have come at an unexpected cost, according to a report today.
London24 are reporting that the signature of Byram has pushed West Ham above their threshold for Financial Fair Play regulations - which would mean any potential pursuit of a new striker looks highly unlikely at this time.
West Ham would therefore seem likely to push a few players out of the door this month - and that does seem the case.
Mauro Zarate looks set to join Fiorentina whilst West Ham are also believed to be open to offers for Nikica Jelavic.
So hopefully West Ham will be back on an even footing financially by the end of the month.