Swansea City have been denied international clearance by Fifa for transfer deadline day signings Darnel Situ and Rafik Halliche.
The Premier League side had agreed to sign Situ from Lens as well as a loan deal for Fulham's Halliche.
But they have been informed they will not be granted international clearance for either defender.
Swansea will await written confirmation before considering whether to appeal.
"Swansea City is disappointed with FIFA's decision and are currently pursuing other options to strengthen the squad," the club said in a statement.
"The club will not be making any other comment at this stage until full written clarification is received from Fifa."
The Swans agreed a four-month loan deal for Fulham centre-back
, 25, and a £250,000 permanent deal for
, 19, from French club Lens on 31 August.
Manager Brendan Rodgers had been unable to field the duo whilst awaiting the green light from Fifa due to minor delays in processing the transfers,
Fifa's decision comes despite Swansea having the full backing of the Premier League, the Football Association of Wales, the FA, the French Football Federation and the Professional Footballers Association.
The Swans had already
e for their other transfer deadline day signing Fede Bessone, who returned to the club from Leeds on a free transfer.