The Rangers academy product left Ibrox for Nottingham Forest in July.
The agent of Nottingham Forest's Barrie McKay has slammed ex-Rangers manager Pedro Caixinha over the winger's Ibrox exit.
McKay has excelled for Forest since his July move to England's second tier, in which he has scored four goals and created more [seven] than any other player.
The 22-year-old's form has made a mockery of his £500,000 price tag, and his representative, Grant Smith, has told the Daily Record Forest would have paid more than double that, had Caixinha not relinquished Rangers' leverage.
"Barrie was someone who was going to make them [Rangers] real money," Smith said. "Forest were interested and they made £15m on a player [Britt Assombalonga]. Then Pedro decided not to involve him. Yeah, he ostracised him.
"If I’m in charge of Rangers at that time, I’m asking 'What are you doing?' But what’s Rangers’ leverage [in negotiations]?
"They told them they didn’t want Barrie. If you tell a buyer you want this player to stay - that’s your leverage. Soon as you put him with the youth team then you don’t have any leverage.
"Forest would have paid a lot more. Easily. Double at least. Mark [Warburton, the Nottingham Forest manager] knew him, Davie Weir knew him and they knew the situation. Rangers took their poker hand away from themselves.
"I mean, some of the stuff Pedro said to him... He was contradicting himself all the time. One minute saying he was the best player in Scotland, the next he was putting him with the youths.
"Someone doing the job of that size should have been doing better. He cost Rangers a lot of money."
McKay was reported to be valued at £6 million at the start of the 2017, with Bundesliga runners-up RB Leipzig among those said to be keen.
However, the Scotland international's value plummeted when he failed to sign a new contract at Rangers, as he approached the final 12 months of his existing one.
Caixinha, who had replaced Warburton at Ibrox in March, was sacked by Rangers last month after a disastrous spell in Glasgow.
The Portuguese coach is said to have turned down a move to former club Santos Laguna in Mexico.