Another said: "I do not see what Ryan Giggs brings to the side at the moment.
"He has been a great servant and got some fantastic goals. But at the moment he's not worth playing. He's no threat."
The calls prompted ex-United stars Viv Anderson and Lou Macari to jump to Giggs' defence.
Anderson said: "I still think Ryan Giggs is a threat at times.
"I'm surprised at this stage of the season people pick on players who've been here a long time."
Macari added: "The manager picks him because he feels he's the best man for the job.
"Players can have off days or periods when you are having a nightmare."