Talisman Neymar is still recovering from an ankle injury suffered in their opening win against Serbia, and they have only one specialist full-back available after left-back Alex Telles suffered a knee injury during the Cameroon defeat.
Starting full-backs Danilo and Alex Sandro have been out after injuries suffered earlier in the competition. Their availability is still unclear.
Telles and forward Gabriel Jesus, who also suffered a knee problem against Cameroon, were officially ruled out for the rest of the tournament by the Brazilian FA on Saturday.
With their ticket already booked for the next round after two wins, coach Tite on Friday made nine changes to the team that won 1-0 against Switzerland in game two, leading to Brazil's first loss to an African nation in their World Cup history.
"The physical demand is ever increasing, the time is short, it's a cumulative effect of games and sometimes you don't have the ideal recovery time on your hands," Tite said on Friday.
"I don't really know what to say other than that, mentally, the cup is very demanding. It drains you.
"The intensity of the matches, the preparation - they are components of analysis that we have to delve into deeper, but they are all considerable."
Brazil's Saturday training session was not open to media, but Tito said Neymar, Alex Sandro and Danilo would be on the pitch to test their condition.
If neither defender can play, centre-back Marquinhos may switch to the left, with 39-year-old Dani Alves - who became the oldest Brazilian to start a World Cup match when he featured against Cameroon - could slot in on the right.
If Tite opts to use Real Madrid centre-back Eder Militao as a full-back, as he did in the absence of Danilo against Switzerland, Brazil would have no other defenders on the bench.
If Neymar is still out, Real Madrid prodigy Rodrygo is likely to be Tite's first option. The pairing of Fred and his Manchester United teammate Casemiro in the midfield that Tite used against Switzerland was less than convincing.
Newcastle's Bruno Guimaraes could also be an alternative, pushing Lucas Paqueta forward into a playmaking role.
South Korea will rely on talisman Son Heung-min to lead them against the odds-on favourites on Monday (6am Tuesday AEDT), after he ran himself into the ground on Friday to ensure his team reached the last 16 with a dramatic come-from-behind 2-1 win over Portugal.
The Koreans are the only Asian side to have reached the semi-finals before, when they were co-hosts with Japan in 2002, and they will be hoping to shock Brazil on Monday to make history again.
