Roy Hodgson is optimistic Alex Oxlade-Chamberlain will be fit to go to the World Cup despite knee ligament damage.
Oxlade-Chamberlain fell awkwardly after a clumsy challenge by Carlos Gruezo in England's 2-2 draw against Ecuador at Sun Life Stadium in Miami on Wednesday night.
Scans taken on Thursday showed the Arsenal midfielder suffered medial ligament damage to the right knee.
It is understood Oxlade-Chamberlain only sprained the ligament and did not tear it. He is expected to be out for two to three weeks.
He is therefore unlikely to play a part in England's first two group matches, but that may not stop him from travelling to Brazil with the squad on Saturday night.
Speaking at a Vauxhall-sponsored England fans' forum, England manager Hodgson said: "We will do everything in our power to keep him (in the squad). Our medical team are optimistic and he is optimistic.
"We can't say how long for certain it will take him to recover but obviously he will get very extensive treatment.
"We have the right to replace him if we want to up to 24 hours before the first game.
"We will do everything we can to keep him with us because: a) we would we like to think we might go beyond the group stage although we can't guarantee it, we are certainly planning for it.
"And b) he played so well yesterday. He was undoubtedly our best player in the time he played and it would be a major blow if we lose him."
Oxlade-Chamberlain put in a strong performance against Ecuador and last June he scored a stunning goal in the Maracana against Brazil.
Being ruled out after just returning from a groin injury would be a big blow to the former Southampton winger, but he is refusing to get down about the injury.
"Gutted to have picked up an injury yesterday," Oxlade-Chamberlain tweeted.
"I'm staying positive and getting to work with the medical team on recovery.. Fingers crossed!''
Oxlade-Chamberlain joined his team-mates for a recovery session at the squad's base in Barry University in Florida on Thursday, although he was wearing a leg brace.
The 20-year-old was able to walk relatively freely despite the injury to his right knee, which buckled under the pressure of Gruezo's foul in the 63rd minute.
Before the injury, Oxlade-Chamberlain looked to have greatly improved his chances of lining up against the Italians in Manaus on June 14.
The England manager said: ''He was excellent. He was back really to his best so all I can do now I suppose is cross my fingers and touch every piece of wood I pass by that it is not serious.''
Hodgson has several options should he decide to drop Oxlade-Chamberlain on injury grounds.
Manchester United midfielders Michael Carrick and Tom Cleverley are on England's standby list, but they have not spent a minute with the squad this summer.
Carrick has been on holiday in Ibiza while Cleverley was pictured at the races with his girlfriend on Wednesday.
Unlike Carrick and Cleverley, John Stones and Jon Flanagan have been with the squad ever since Hodgson announced his World Cup squad.
The defenders were brought along to Portugal and Miami as cover for Phil Jones, who suffered a shoulder injury in the final week of the domestic season.
Both players can operate at right-back, which would allow James Milner, who filled in there on Wednesday, to concentrate on playing in his normal midfield role.
Stones, who earned his first cap against Peru, and Flanagan, who made his bow off the bench against the Ecuadorians, have both enjoyed their time with the squad as standby players.
''It doesn't get much better than coming away with your country,'' Flanagan told TheFA.com in a joint interview with Stones on Tuesday.
''There are top players from all around the country, so training with them is really good.''
Everton defender Stones, who only made his first Premier League start in January, said: ''It's been such a good experience. It has given us that hunger to keep on improving and hopefully when that next England squad comes around we'll gets the call."
Jones and Chris Smalling, playing together for the first time for England, looked vulnerable to the pace and power of the Ecuadorians on Wednesday, but Hodgson was happy with their efforts.
''The two centre-backs did extremely well,'' the former Liverpool manager said.
''You always will struggle in moments against teams like Ecuador with their pace and technique but we created a large number of opportunities where we were attacking. What we have to make certain is that we shore up a little bit better behind some of these attacking movements and make certain it doesn't go directly against our back four.''
Hodgson received some good news on Thursday after FIFA confirmed Raheem Sterling will be available for the Italy game, as he will serve his one-match suspension during Saturday's game against Honduras.