The United manager opted against turning to the 29-year-old striker on Monday night despite a 2-1 loss to Arsenal in FA Cup quarter-final at Old Trafford.
He may have lost the player now and I will be very surprised if he plays a role between now and the end of the season
The Colombia international, who joined the club on a season-long loan last summer, was forced to drop down to the club’s reserves side for their match against Tottenham Hotspur on Tuesday night.
Former Liverpool and Manchester City midfielder Hamann was shocked by Van Gaal’s decision to humiliatingly demote Falcao to the club’s second string.
“He has been fit for eight weeks and to stick him in there is a disgrace,” Hamann told talkSPORT on Wednesday morning.
“Don’t you think he deserves a little bit more respect from the manager? Putting him in the Under-21s is the ultimate demotion you can face as a senior player.
“I played games [for the reserve side] when I was injured and it was not a problem. But when you are not in the team and have been fit for six to eight weeks and have been put in there, that is the ultimate demotion.
“The best players have got huge belief in their own ability and they have got a certain standing and you can’t treat a Falcao like you treat a Chris Smalling or Jonny Evans.
“He may have lost the player now and I will be very surprised if he plays a role between now and the end of the season.”
The 29-year-old arrived at Old Trafford on loan from Monaco last summer with a reputation as one of Europe’s top strikers.
However, he has only managed to score four goals in the Premier League and has not found the net since the 3-1 win over Leicester back in January.
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