United have until May to activate a £40m buy-out clause but it is not certain they will proceed.
"The truth is, right now, we don't know what will happen," said Falcao's agent Jorge Mendes.
Falcao has already decided he will not be returning to Monaco. Ideally, he would prefer to stay at United.
However, Falcao did not even make Louis van Gaal's 18-man squad for the 1-0 home defeat by Southampton on 11 January.
United boss Van Gaal said afterwards there was no injury problem and the decision was based purely on his selection of the players he felt were best suited to the game.
The move has perplexed and angered those close to the player, who has scored three times in 13 appearances for United, only eight of which have been starts.
"It is very difficult for Manchester United fans," said Mendes.
"They have an absolutely brilliant player, one of the very best in the world, who would without any doubt play 90 minutes of the match, every time, with any other club.
"What we do know is that he will play in one of the very best clubs in the world next season, whether that is Manchester United or not."
Daley Blind returned to play 90 minutes on Sunday after injuring a knee in November.
"The places in the team are expensive, and the manager has said that as well," he said. "So you have to train, every day, very hard to show yourself and show that you really want to play."
