Brazil defender Dani Alves will be out for at least three weeks after injuring his anterior cruciate ligament, Paris Saint-Germain have confirmed.
Alves, who turned 35 earlier this week, may yet need surgery after injuring his knee in the final of the Coupe de France on Tuesday night, which PSG won 2-0.
The former Barcelona full-back will be reassessed after a minimum of three weeks, the club said.
The 2018 Russia World Cup kicks off on June 15, with Brazil's first group game two days later against Switzerland.
Alves, who joined PSG from Juventus last summer, was Brazil's first-choice right back at the 2014 World Cup in his home country. He has 107 caps and has scored seven times.
PSG forward Neymar is also in a race to get fit for Brazil at the World Cup after breaking a bone in his foot.
He returned to Paris this week to complete the final stages of his rehabilitation.