Brazil appealed against Neymar's remaining international suspension but CAS has upheld the ban, meaning he will not face Chile or Venezuela.
The Court of Arbitration for Sport (CAS) has rejected an appeal to have Neymar's two-match ban for Brazil lifted.
The Barcelona star was handed a four-match suspension for competitive internationals following a red card against Colombia at the Copa America earlier this year.
The Brazilian Football Confederation (CBF) had asked for the remaining two matches of the ban to cover only Copa America fixtures, but CAS announced on Friday that it has upheld its initial decision.
"By rejecting CBF's appeal, the two remaining match bans will have to be served during the next qualifying matches for the 2018 FIFA World Cup Russia to be held on October 8 and 13 2015," read a CAS statement.
Neymar will consequently be forced to miss the games with Chile and Venezuela as South American World Cup qualifying gets underway this month.
CAS went on to confirm it would explain the decision to reject the CBF's appeal at a later date.