Brazilian team doctor Rodrigo Lasmar said on Monday that forward Neymar is recovering well from the knee surgery.
The star winger had suffered the injury last month but a timeline of when he will be able to return to action is still uncertain.
Neymar underwent surgery earlier this month in a Belo Horizonte hospital after he ruptured the anterior cruciate ligament (ACL) and meniscus in his left knee on international duty.
"He's shown, from the first moment that he's following what we're proposing. He knows that it's a process that he's going to need all of us, physiotherapist, fitness trainer, so that we can have Neymar (back) as soon as possible," said the doctor.
Lasmar, who conducted the surgery, didn’t set a date for the Al-Hilal player's return.
"Injuries are individual. In general, there are associated injuries that can be just as important, such as a meniscus injury. All this makes the procedure more complex, with a slower recovery period. That's why we don't talk about a timescale," he said.
Neymar moved to the Saudi Pro League in August for a reported 90 million euros, but the former Barcelona and Paris St Germain forward only played five games because he was struggling with muscle injuries.
Brazil, who are placed at the third position in the South American World Cup qualifying standings with seven points, will lock horns with fifth-placed Colombia, with six points, on Thursday. They host leaders Argentina, who have 12 points, the following Tuesday.
Lasmar also said goalkeeper Ederson had withdrawn from the squad due to an injury he sustained playing for Manchester City in their 4-4 draw at Chelsea in the Premier League on Sunday.
"He suffered trauma to his foot in the final minutes and was able to continue the match but the pain became intense. The foot became swollen, making it difficult to walk," Lasmar said.
Athletico Paranaense keeper Bento has been called up to replace him in the Brazil squad.