Dec 8 (Reuters) - Neymar will undergo knee surgery after playing through the pain to help Santos avoid relegation with a 3-0 win over Cruzeiro on Sunday, raising more doubts about the winger's chances of playing at next year's World Cup.

The 33-year-old returned to his childhood club Santos in January after a stint in Saudi Arabia and had a crucial impact in his team's survival in the Brazilian top flight, scoring five goals in the last four matches.