Davies had been racing against time after he was almost killed in a car accident last October but his hopes of going to South Africa were dashed when he failed to make the initial 30-man squad which will be trimmed to 23 on June 1.
"Charlie has shown incredible heart and determination to reach this point in his recovery," U.S. head coach Bob Bradley said at the announcement.
"We have followed his progress extensively during the past several months through physical examinations and personal observation by our staff and he remained in consideration for this training camp until yesterday."
Davies suffered multiple fractures and internal injuries in the car crash last year that claimed the life of another passenger. He defied incredible odds to resume light training with his French club Sochaux but ran out of time for the World Cup.
"FC Sochaux notified us that at this point Charlie has not been given medical clearance, and that they would not grant his full release to join the camp," Bradley said.
"Given that status and our own evaluation of his progress, we feel it is Charlie's best interest to continue his rehabilitation and focus on getting fully prepared to resume his professional and international career."
While Davies was overlooked, two other players, Oguchi Onyewu and Stuart Holden, were both given the benefit of the doubt and included after only recently returning to their clubs from injury.
Houston striker Brian Ching, who was picked for the last World Cup but did not play a match, was also retained despite currently being sidelined with a hamstring problem while experienced midfielder DaMarcus Beasley was selected for his third World Cup despite struggling for game time with Rangers.
Edson Buddle of the Los Angeles Galaxy was rewarded with a place in the squad while Herculez Gomez got the nod after moving to Mexico this year and becoming one of the leading scorers.
Central midfielder Kyle Beckerman was a surprise omission after playing well in the domestic Major Soccer League, which provided around a third of the players in the squad with the bulk based overseas.
"We feel we've put a very good group together," Bradley said.
"Obviously a lot goes into qualification and many players are involved. It's not always easy to get down to 30, but we feel very good about the group we have."
The U.S. have been drawn in Group C at the World Cup with England, Slovenia and Algeria.
They are due to play warm-up matches at home against Turkey and Czech Republic before finalising their roster and heading to South Africa for a final tune-up against Australia.
Goalkeepers: Brad Guzan (Aston Villa), Tim Howard (Everton), Marcus Hahnemann (Wolverhampton)
Defenders: Carlos Bocanegra (Rennes), Jonathan Bornstein (Chivas), Steve Cherundolo (Hannover), Jay DeMerit (Watford), Clarence Goodson (IK Start), Chad Marshall (Columbus Crew), Oguchi Onyewu (AC Milan), Heath Pearce (FC Dallas), Jonathan Spector (West Ham United)
Midfielders: DaMarcus Beasley (Rangers), Alejandro Bedoya (rebro), Michael Bradley
