The Macedonian left-back had been due to make his debut in last night’s defeat against Burnley but had his move to the Reebok vetoed by the footballing authorities late on Monday night.
West Brom agreed to allow the 29-year-old left-back out on a short-term loan despite having loaned him themselves at the start of the season from Dynamo Kiev.
Popov had travelled to the North West for a medical and was ready to end Dougie Freedman’s long search for defensive cover, only for the Premier League and Football League to voice their concerns.
As the deal was agreed outside the regular transfer window, the authorities deemed it an international transfer rather than an emergency loan and so put the blocks on the move.
But Wanderers were working hard to salvage the loan yesterday – and sources in the Midlands were upbeat about it going through before the weekend, when Wanderers face Millwall at The Den.
Popov has started just one Premier League game for West Brom this season, with five appearances in all competitions.
He featured more regularly for the Baggies last season before falling behind Liam Ridgewell in the pecking order.
Boasting experience in the top flight, Ukraine and in Holland with Heerenween, Freedman hopes he can have a stabilising effect on a back four that has lacked a genuine left-back since Marc Tierney broke his leg playing against Yeovil in October.
Speaking after last night's 1-0 defeat to Burnley, Freedman revealed that the club had appealed the decision to block the loan.
"It's with the lawyers right now," he said. "We'll wait and see what happens."