Cavani left out of Uruguay squad for World Cup qualifiers
The 33-year-old, who scored a record 200 goals for PSG, is without a club after his contract with the French champions ended in June.
"Beyond the fact that we all know the capacity that Edi has, this pandemic has interrupted his training regimen," said Rebollo.
Cavani's last match for PSG was a Champions League game on March 11, as the coronavirus pandemic swept through Europe.
Coach Oscar Tabarez told AFP last month Cavani would still feature during the long South American qualifying campaign for Qatar 2022.
"Cavani will be there! Because he is a very important player, and that weighs heavily on any decision" said Tabarez.
Cavani has scored 50 goals in 116 appearances for Uruguay. He has formed a long-standing international strike partnership with Atletico Madrid's Luis Suarez, who is from the same town on the Argentine border and is three weeks older.
Tabarez's side face Chile in Montevideo on October 8 before travelling to Quito for the clash with Ecuador at altitude five days later.