The forward suffered what O Globo describes as a near-total muscle rupture in his left thigh during Chelsea's defeat to Manchester United last weekend — a more severe diagnosis than early reports suggested.
Surgery has been ruled out, a decision taken specifically to preserve any chance of Estevão featuring at the World Cup.
Brazil open their group stage campaign against Morocco on 13 June. Head coach Carlo Ancelotti is expected to name his squad on 18 May, and sources within the Brazilian Football Confederation have indicated expectations are low given the severity of the injury.
This is Estevão's fifth injury absence of the season and his second hamstring problem in the space of two months, having missed 25 days earlier this year with a similar issue.
Chelsea interim head coach Calum McFarlane confirmed the teenager "won't play for us this season" ahead of Sunday's FA Cup semi-final against Leeds United.
From the club's perspective, the priority is protecting a long-term asset whose career at Stamford Bridge is only just beginning. Shared control of his recovery — with Chelsea and the CBF both monitoring progress — reflects the tension between those competing interests.