Algeria, Ghana and African champions Cameroon face a crucial week of 2018 World Cup qualifiers.
Cameroon coach Hugo Broos admits their campaign is doomed if they do not take at least four points off Nigeria in back-to-back clashes.
The Group B rivals meet in Uyo on Friday and then in Cameroon’s capital Yaounde three days later.
“Should we fail to achieve that target, I do not think it will be possible to qualify for Russia,” Broos said.
Nigeria top the group with six points after two rounds, Cameroon have two and Zambia and Algeria one.
Broos is hoping for an away draw and a home victory that would reduce the gap between the countries to one point.
The final two qualifiers will be played in October and November with only the five group winners progressing to play in Russia.
“My players need little or no reminding of how important the matches against Cameroon are,” said Germany-born Nigeria coach Gernot Rohr.
Algeria, who have qualified for the last two World Cups, are in Lusaka to face Zambia on Saturday.
Ghana, seeking a fourth consecutive World Cup appearance, host Congo Brazzaville in Kumasi Friday needing maximum points to have any realistic hope of overtaking Group E leaders Egypt.
The Pharaohs have six points and the Black Stars only one with Uganda between them on four.
Ghana coach Kwesi Appiah called up long-time campaigners like the Ayew brothers, Andre and Jordan, and Asamoah Gyan, and also named five uncapped players.
Egypt are away to Uganda on Thursday in a repeat of a 2017 Africa Cup of Nations group match in Gabon won 1-0 by the north Africans thanks to a last-gasp Abdallah Said goal.
Said is in the squad, and so is 44-year-old goalkeeper Essam El Hadary, as Egypt seek a win after losing the 2017 Nations Cup final to Cameroon and a 2019 qualifier in Tunisia.
South Africa accept that hopes of a fourth World Cup appearance could hinge on defeating Cape Verde twice in Group D, starting in Praia Friday.
Bafana Bafana will take encouragement from the fact that Cape Verde have lost competitive matches there against Morocco, Libya and Uganda since last year.
Cape Verde on the other hand will be aware of the goalkeeping problems that South Africa are facing.