"Qatar is a possibility," the source said, with Dec. 8 the most likely date.
CONMEBOL are expected to make an official announcement later on Thursday at their headquarters in Paraguay.
The organisation's independent Disciplinary Tribunal is also due to hear Boca's appeal this Thursday to award them the game because of violence by River fans, throwing the future of the match into further confusion.
Argentina's two biggest teams drew the first leg 2-2 at Boca's ground on Nov. 11 and were due to play the decisive second match at River's Monumental stadium last Saturday.
However, Boca's players were hurt when River fans attacked their team coach as it approached the stadium and the game was first delayed until Sunday and then postponed indefinitely.
The violence was an embarrassment for Argentina just days before this weekend's G20 summit in Buenos Aires.
Qatar has been mooted as a possible venue after CONMEBOL ruled out holding the match in Argentina due to security concerns.
The winner of the Libertadores, South America's equivalent of the Champions League, will represent CONMEBOL in the Club World Cup in the United Arab Emirates just days later.
The tournament kicks off on Dec. 12 with the South Americans playing their first match on Dec. 18.
(Reporting by Andrew Downie; Editing by Toby Davis)
