Portugal and Uruguay will battle it out for the 20th and final qualifying spot for the World Cup.
They will face each other in a two-leg play-off, starting in Lisbon on 10 March and in Montevideo on 24 March.
The winner will go forward to Pool C along with New Zealand, Scotland, Italy and Romania.
Tonga play South Korea in Auckland this weekend to decide the 19th and penultimate spot.
France hosts the World Cup from 7 September until 20 October.
