The Colombia international had hoped to return for Saturday's 2-1 win over Arsenal but manager Louis van Gaal later revealed that he expected him to be out for a further two weeks with a new injury.
Falcao has not featured for the Red Devils since their 2-2 draw with West Brom on October 20 and is yet to complete 90 minutes for his new club since his summer move.
However, the striker wrote on Twitter: "Back to training 100 per cent and ready to help the team in the next games.”