Barry suffered an ankle injury playing against Tottenham on 5 May
England coach Fabio Capello has given midfielder Gareth Barry another week to prove his fitness for the World Cup.
The 29-year-old player underwent tests on an ankle ligament problem on Tuesday after suffering the injury playing for Manchester City on 5 May.
Capello has to name his 23-man squad on 1 June, ahead of their World Cup opener against the United States on 12 June.
The Italian has insisted he would not include anyone in his final squad if they were unfit to play in the US game.
And the 63-year-old knows the importance of the Manchester City man to his World Cup plans.
"Barry always played with me," said Capello.
"After Owen Hargreaves it was Gareth Barry. He is one of the important players, really important.
"If Barry is fit, he will come with us. If not, he will stay at home. He is one of the players we want to be fit."
One potential safety net for England is the Fifa rule which allows managers to replace any injured players up to 24 hours before the first game.
However, the former Real Madrid and Milan coach is clearly giving Barry, who has started 19 of the 22 England matches the Italian has overseen, every chance of proving his fitness.
It was initially thought Barry had an appointment with his specialist on Tuesday to assess his recovery, but instead the former Aston Villa midfielder will undergo a series of rigorous tests on the injury he picked up against Tottenham in the Premier League.
If Barry does not prove his fitness, Capello could turn to Aston Villa's James Milner - recently crowned as the Professional Footballers' Association young player of the year - or Michael Carrick of Manchester United to occupy the role normally filled by Barry, while West Ham's Scott Parker is also a possible option.
But Capello admits he is reluctant to ask Liverpool's Steven Gerrard to fill the breach.
"Steven is really dangerous when he gets close to the box," said Capello.
"If he has to play in the same position as the other midfielders he is good, but he is too far from the box. He has to get between two lines, the back four and the midfield. That is where you go to shoot.
"I am lucky because his performance level is always high, but while I like to go forward you always need a holding player in front of the back four."
The England manager has also been looking into the possibility of switching to a three centre-back system although he played with two central defenders in the 3-1 friendly victory over Mexico at Wembley on Monday night - starting with Manchester United's Rio Ferdinand and Tottenham's Ledley King.
England's players will now return to Irdning in the Austrian Alps for further training before playing a final warm-up game, against Japan, on Sunday.