The 18-year-old was forced off after 16 minutes at Stamford Bridge and was visibly distressed at half-time.
Head coach Liam Rosenior said: "He was devastated. He was crying at half-time. I'm really devastated for him."
Scans confirmed the extent of the injury, which is worse than initially feared. A grade four strain is the most severe classification and typically requires several weeks of rehabilitation.
Brazil's opening World Cup group stage match against Morocco is on 13 June, leaving limited time for recovery.
Sources close to Estevão told BBC Sport he will be fit to feature in the tournament.
However, ESPN Brazil reports there is active debate within the Brazilian Football Confederation about whether to include him in the squad named on 18 May in the hope he would be available for the knockout stages.
Head coach Carlo Ancelotti had previously said without hesitation that Estevão would be part of his World Cup plans.
This is the third muscle or hamstring problem the teenager has suffered since December.
He has made 36 appearances for Chelsea this season, scoring eight goals and providing three assists — a workload that has raised questions about how much his body has been asked to do in his first year of European football.