(Adds Telles and Jesus out for rest of World Cup)
By Fernando Kallas
DOHA, Dec 3 (Reuters) - World Cup favourites Brazil are racing to overcome injuries to key players as they prepare for their last-16 match against South Korea on Monday, after a heavily changed side lost 1-0 to Cameroon on Friday night.
Neymar is still recovering from an ankle injury suffered in their debut win against Serbia, and they have only one pure full back available after left back Alex Telles suffered a knee injury in the Cameroon.
Starting full backs Danilo and Alex Sandro are out after injuries suffered earlier in the competition and their availability is still unclear.
Telles and forward Gabriel Jesus, who also suffered a knee injury 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, Tite on Friday made nine changes to the team that won 1-0 against Switzerland, leading to Brazil's first loss to an African nation in its 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," coach Tite told a news conference 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."
Tite did not let media attend their training session on Saturday but said Neymar, Alex Sandro and Danilo should be on the pitch to test their condition.
If neither can play, centre back Marquinhos could perhaps switch to the left and 39-year-old Dani Alves, who became the oldest Brazilian to start a World Cup match against Cameroon, could be tried out 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 to sit on the bench.
If Neymar is still out, Real Madrid prodigy Rodrygo is likely to be Tite's first option, as the pairing of Fred and his Manchester United team mate 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, 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 on Friday.
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. (Reporting by Fernando Kallas; Editing by Hugh Lawson)