Samir Nasri will be allowed to make his West Ham debut against Brighton at the London Stadium on Wednesday, despite some confusion over new Premier League rules.
Clubs had agreed previously that no new players registered at the start of the window would be eligible to play in January's first round of matches.
However, because Nasri was out of contract, signed last week outside of the transfer window and the Hammers had space in their Premier League squad list, the Frenchman is available for selection.
It means the midfielder could make his first appearance for Manuel Pellegrini's side against Brighton rather than wait for Birmingham in the FA Cup this weekend.