Everton confirm McCarthy double leg break
McCarthy suffered the horrific injury 10 minutes after the interval as he was attempting to block Salomon Rondon's shot inside the penalty area, with the West Brom forward kicking his planted standing leg at full force.
The Republic of Ireland international was attended to by medical staff for more than seven minutes, while a clearly distraught Rondon had to be comforted by his team-mates.
Speaking after the game, Allardyce said: "James has fractured his tibia and fibula. He's paid a heavy price for his bravery and commitment. It's a big blow for him and us.
"It's a loss to us from now until the end of the season, it happens in the game of football but not often that severe.
"It was our own fault and our own stupid play in that area, James recovered brilliantly to stop a goal but suffered because of it."
West Brom had taken an early lead through Jay Rodriguez's fourth Premier League goal of the season, but Allardyce's side pulled themselves level in the 70th minute through Oumar Niasse's first touch of the game.
The Senegal forward had only just been introduced for the ineffective Cenk Tosun when he met debutant Theo Walcott's precise back-post header to thunder a volley into the roof of the net, ending the hosts' run of three straight Premier League defeats.
| All our thoughts are with James McCarthy this evening after it was confirmed he has suffered a double leg fracture. #GetWellSoonJames pic.twitter.com/JpEEIBrKcJ
— Everton (@Everton) January 20, 2018