Drake took to Instagram Monday to let his fans know he was "truly devastated" the show's getting postponed ... and promised they'll reschedule for the soonest date possible. October World Weekend -- which also was to serve as a Young Money reunion -- was to feature Nicki Minaj and Lil Wayne.

In his announcement, Drake also said, "... I hope everyone stays safe and healthy and I love you all I am so sorry for letting you down on our weekend together and the moment I test negative I will give you everything I got onstage (except the Covid)."

Drake had just partied with Nelly Furtado during the OVO event ... with other surprises planned throughout Toronto.