Italy coach Cesare Prandelli went to London hoping to put the finishing touches on his World Cup squad but left with a hole in his midfield.
AC Milan captain Riccardo Montolivo was lost for the tournament in Brazil after fracturing his shinbone in his left leg following a challenge from the Republic of Ireland's Alex Pearce during Saturday's goalless draw at Craven Cottage.
"Montolivo has a fractured shinbone," Italy team doctor Enrico Castellacci said. "I will evaluate the extent of the injury once I see the X-ray but almost all tibia fractures need surgery.
"He will probably need at least two months to recover; hence, he will miss the World Cup."
Montolivo will travel on Sunday morning with an air ambulance to Milan while the rest of the Azzurri team heads back to Italy's headquarters in Coverciano, Florence.
"We know that this is part of football but we are all shocked," Prandelli said. "Our thoughts are with Riccardo.
"He is an important player for us and has been, in the past few years, an example to all his team-mates, not only on the pitch but off it."
The injury to Montolivo overshadowed the game against the Republic.
"The game was conditioned by Montolivo's injury," Prandelli said.
"We had started the game so well and things were looking good but once that happen, my players were affected psychologically.
"I will decide after Sunday's training session whether to take 24 hours more to name the final squad."
Prandelli is considering adding two more players to his travelling party to Brazil.
Italy can replace any player in the squad up to 24 hours before their opening game against England in Manaus on June 14.
"I may take one or two more players (besides the 23) to Brazil," he said. "But we will see."
Prandelli was at least boosted by Torino defender Matteo Darmian, who made his senior debut against Ireland and boosted his World Cup claims.
"I'm really happy for Matteo," Prandelli said. "He had a fantastic debut and he did really well."
Giuseppe Rossi was another player who was looking to impress.
The Fiorentina striker, who recently returned from a right knee injury that had sidelined him for four months, played for 70 minutes against Ireland and created several chances.
"I felt good on the pitch," Rossi said. "We had our chances although at the end, we were a little bit tired from the work we had carried out in training this week."
Italy face Luxembourg on Wednesday in Perugia in what is their final warm-up before travelling to Brazil.