Leeds United reportedly could face a transfer embargo over their contract dispute with Blues winger Cameron Stewart.
Stewart was due to join the Whites from Hull City last summer after a loan spell but the Yorkshire club pulled out of the deal.
In May, the 24-year-old was awarded £800,000 following an FA arbitration hearing held the previous month.
Now, according to the Daily Mirror, the PFA are planning to request that the Football League prevent Leeds from signing any further players until the cash is paid and the matter resolved.
Stewart and Leeds signed a three-year deal which was due to come into effect last July at the end of his contract with Hull City, after a 93-day loan at Elland Road at the end of 2013/14.
However, by the time the contract was lodged with the Football League not all the signatories were still at the club, including former managing director David Haigh, who had moved on in the April after falling out with club president Massimo Cellino.
Cellino then refused to get the paperwork re-signed, pulled the plug on the deal and subsequently claimed that the contract was invalid.
The matter eventually went to the FA hearing with Stewart successfully claiming the West Yorkshire club owed him £800,000 in unpaid wages, the difference between the cash he is being paid at Town and the higher sum he would have received under his Leeds deal.
After his move to Elland Road broke down Stewart joined the Blues, signing a three-year contract.
Having broken his jaw late in pre-season, the former Manchester United trainee was unable to win a place in the Town side and his only Blues appearances to date are the two sub appearances in the FA Cup ties against Southampton. Late last season he joined Barnsley on loan.
Stewart was back at Playford Road for pre-season training on Tuesday with manager Mick McCarthy not ruling him out of his plans: "He’s got to get his nose down and see if he can get in the team, see if he can get in the squad first.”
Meanwhile, Middlesbrough’s pursuit of Daryl Murphy continues to fill column inches with the Daily Mail the latest source to report that the Teessiders will come back with an improved offer for the 32-year-old Irishman, the Blues having previously turned down a bid of £4.5 million.
Former Spurs striker Daniel Akindayini, 19, who was on trial with the Blues towards the end of last season, has joined Brighton and Hove Albion.
Ace Howell, 18, who joined the Town academy from Needham Market on a short-term deal earlier in the year, has moved on to Bury Town.
Elsewhere, former Blues striker Jon Stead, 32, has signed a two-year deal with Notts County after leaving Huddersfield.
Ex-Town winger Jack Doherty, 20, has joined Longford Town from hometown club Waterford United.
Reported Blues target Paul McShane has completed his move to Reading having been released by Hull City at the end of last season. The 29-year-old Irish international has signed a three-year deal.