Capello and his assistant Franco Baldini were checking on the fitness of several players on Monday before settling on the 30 they will take to Austria.
It is understood Capello is only prepared to pick players who are fit and will be ready for England's first match against the United States in Rustenburg on 12 June.
Rooney, who saw Chelsea's Didier Drogba overtake him for the Premier League's Golden Boot award, limped off after 77 minutes of United's last game of the season.
He was able to join his team-mates on a parade lap at Old Trafford following the culmination of United's season and assistant manager Mike Phelan added: "He should be OK so all the phone calls and worries can be dispelled straight away.
"It was a precaution and I think Wayne can look forward to the World Cup."
There is, however, a major fitness concern over Manchester City midfielder Gareth Barry, who injured an ankle during his side's defeat by Tottenham last Wednesday.
King has played three matches in nine days for Tottenham
If, as anticipated, he is ruled out for three more weeks, Barry will miss the training camp and the games against Mexico and Japan.
England received a boost on Sunday when captain Rio Ferdinand played a full 90 minutes in United's 4-0 victory over Stoke following a groin injury.
Ferdinand's injury-hit season - along with the hamstring complaint that saw Manchester City's Joleon Lescott miss the end of the campaign - has forced Capello into considering alternative centre-half options.
Tottenham pair Ledley King and Michael Dawson are both thought to be in the frame, while Baldini has reportedly been in talks with Liverpool's Jamie Carragher, who is also capable of operating at full-back, about coming out of international retirement.
While Dawson is yet to gain any international experience, King has 19 caps to his name and despite being plagued by persistent knee problems, he has produced a string of superb performances in helping Spurs finish fourth in the Premier League.
"Towards the end of season Ledley has played a lot more, proved his fitness and been fantastic," King's Tottenham team-mate Peter Crouch, who is set to be included among the strikers, told BBC Sport.
Crouch talks up King's World Cup chances
"For me, when he is fit he is the best centre-half around, he is a fantastic player. He has come through three games in nine days (against Bolton, Manchester City and Burnley) and I cannot remember the last time he did that."
Carragher has 34 caps and Crouch, who was a team-mate of his at Liverpool from 2005-2008, has no doubt the 32-year-old could come in and do a job.
"He has been a top-class centre-half for a number of years, played in Europe and got a hell of a lot of experience. If selected he is not going to let anyone down," he added.
The return to fitness of Chelsea midfielder Joe Cole and Spurs winger Aaron Lennon will be a relief to Capello, but the situation with Manchester United's Owen Hargreaves is less clear.
Hargreaves starred for England at the 2006 World Cup in Germany but a chronic knee problem has limited him to only one appearance since September 2008.
The 29-year-old came on in the 89th minute of United's recent win at Sunderland and was due to face Stoke on Sunday, only to fall victim to a virus on Saturday night.
Former captain David Beckham will definitely miss the World Cup with a ruptured Achilles tendon but the LA Galaxy midfielder may yet join up with the squad in South Africa to assist Capello and his staff.
"He's so experienced," Crouch said of the 35-year-old. "He has captained his country so many times that I'm sure if he was there he'd be a big support for all the lads."
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