Having agreed a fee with Rosenborg, personal terms and seen Gamboa pass a medical, Irvine is now waiting for the Costa Rica international's hearing to take place in front of a Football Association panel.
The midfielder played in all five games at the World Cup as the Central Amercian nation exceeded expectations to reach the quarter-finals in Brazil.
His performances for Jorge Luis Pinto's side alerted Albion and Irvine remains positive they will be able to complete the deal in the near future.
"We're not in control, it’s out of our hands," he told the club's official website. "But I think it would be amazing if we didn't get this one over the line.
"Cristian has played just over 70 per cent of the games for his country, but they’ve factored into those figures a non-FIFA ranked tournament which his club stopped him going to.
"They kept Cristian back to play in some league games."
Gamboa joined Rosenborg on loan from Copenhagen in 2012 before completing a permanent deal and has made 52 appearances for the Norwegian club.
