The club 'transfer acquisitions panel' snubbed his list of names to help lift them into the top flight.
Now, City Ground legend Birtles warned: "We can only hope the lack of signings doesn't cost us the ultimate prize of promotion."
Davies, saddled with a small squad, watched Forest scrape a win over struggling Owls.
European Cup winner Birtles said: "If Billy's frustrated, he has every right. This was the big opportunity to back him in the transfer market.
"Forest are neck and neck with Newcastle and West Brom. Newcastle made six signings, West Brom two.
"Forest? Nothing, nil, nada! Billy gave this committee a list of names. He wanted three top additions. Billy's every right to think someone let him down."
Forest boss Billy Davies snapped: "I don't do the buying and selling. I'm a hired hand. I'll continue to do the best I can with players at my disposal."