The 31-year-old Valdes's problem adds to growing injury woes at Barcelona, with Lionel Messi heading a lengthening list on the treatment table.
Medical tests in Barcelona on Wednesday confirmed that Valdes had a torn right calf, the club said in a statement.
"The approximate time off is about six weeks," Barcelona said.
Valdes injured himself while he was striding backwards towards the goalmouth during Spain's loss in Johannesburg on Tuesday, a deflating return to the site of their 2010 FIFA World Cup South Africa™ victory.
Spain's national squad medical services had already diagnosed a torn calf. But further tests were needed to decide how long he would need to recover.
Valdes, who has been in great form, has revealed plans to leave the Spanish champions when his current contract expires in 2014.
During his recovery, Valdes will likely be replaced at his club by veteran Jose Manuel Pinto.
Barcelona announced this month that the 26-year-old Messi would be sidelined for six to eight weeks with a muscle tear in his left hamstring muscle, his third leg injury this season.
Picking up his third Golden Shoe award on Wednesday as the top league scorer in Europe for his 46 goals in the 2012/2013 season, Messi said he was "getting better little by little and luckily there is no more pain".
As for his return to action, "it all depends on how things go. I will be back, but I will not put a date on when," he added.
"My aim is to come back and strengthen my whole body so that nothing goes wrong and I can play without worrying."
Adding to Barcelona coach Gerardo Martino's headaches, Cristian Tello, who sprained his right ankle, and Xavi Hernandez, with a strained muscle in his right leg, have both been declared doubtful for Saturday's match against Granada in the Camp Nou.