Salford-bound forward Tony Puletua has been drafted in to the Samoa squad as a replacement for the injured Reni Maitua.
The news comes as a boost for coach Matt Parish, who had previously had a request to replace Frank Winterstein turned down.
However, with captain Harrison Hansen also ruled out of the tournament through injury, World Cup organisers have ratified a replacement.
A statement said: “In this instance the request has been granted. The basis of this decision was that due to injuries the Samoa squad has been reduced to 21 players.
“The loss of three players in similar positions was considered by the tournament to be exceptional circumstances.”
Puletua, 34, played for Samoa at the 2008 World Cup, and previously won 22 caps for New Zealand.
Samoa, who beat Papua New Guinea 38-4 at Craven Park on last night, travel to Perpignan to play France in their final group game next Monday.
Hansen, Winterstein and Maitua have all now been formally withdrawn from their squad.
Meanwhile, Australia have had a request to call-up a replacement for Luke Lewis rejected.
Lewis was ruled out for the rest of the World Cup after suffering a dislocated shoulder in Saturday’s win over Fiji.