The Australian told the Alan Brazil Sports Breakfast Show on talkSPORT that he has heard rumours of unrest in the United camp, pointing out Welsh veteran Giggs, who is believed to be unhappy with the current situation at Old Trafford.
"It has been obvious for some time that things are not quite right there," said Bosnich.
"I'm hearing very strong rumours that Ryan Giggs has had a falling out with the management and that is a real shame because that is somebody there with exceptional experience. He has been like an institution at Man United, just as much as Sir Alex Ferguson.
"The board have to back the manager while he is employed by the club, but they must be concerned behind the scenes with how things are going. The slide has been absolutely incredible.
"There are things seeping out that things are not well behind the scenes. The fact that a lot of old players are coming out [with criticism], like Paul Scholes, tells me there are definitely problems behind the scenes.
"I mentioned those rumours about Giggs and I don't think he is the only one [who is unhappy] so there are a massive amount of problems there and they need to be sorted quickly."
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