Chapecoense face expulsion from the Copa Libertadores after starting an allegedly ineligible player on Wednesday.
Luiz Otavio was sent off for the tragedy-hit Brazilian club in their previous Copa game, a 3-0 loss to Nacional, triggering a suspension.
But Chapecoense, believing the suspension had been served when Otavio sat out the second leg of the Recopa Sudamericana against Atletico Nacional, started the defender for the Copa match against Lanus.
Otavio scored the winning goal in the 88th minute to seal a 2-1 victory for Chapecoense.
CONMEBOL had warned the club that Otavio was still banned, reportedly for an additional two games, and have now opened an investigation.
The football federation of the Santa Catarina state confirmed that an email from CONMEBOL was sent to the club a week earlier, but ESPN Brasil reported that Chapecoense claimed it was sent to the wrong person and may have even been labelled as spam.
If CONMEBOL rules Otavio was ineligible, it will award Lanus a 3-0 win and dock Chape three points, enough to prevent them from finishing in the top two spots in the group. Chapecoense have vowed to appeal any decision to FIFA, though they only have until Monday to present a case.
Otavio joined Chapecoense on loan in January, six weeks after the plane crash that killed 71 people, including 19 of the club's players.