Russian club Lokomotiv Moscow have confirmed the death of 18-year-old player Alexei Lomakin.
Lokomotiv have said they are "shocked by the tragedy" of the midfielder, who played for Lokomotiv's youth team and "details of the tragedy are being cleared up," without providing further details.
Russian media earlier reported that Lomakin's mother had reported him missing.
He had been undergoing medical treatment for an injury sustained last month.