The England international has long been linked with a big-money move to Manchester City this summer but there is a doubt over that now as the club could not agree a deal with the defender.
City boss Pep Guardiola is now being heavily linked with a cut-price reunion with the 34-year-old Dani Alves from Juventus instead.
Reports in Germany over the weekend claimed that Bundesliga champions Bayern Munich were now the frontrunners to land the England international.
Walker is valued at around the £40m mark but his place as a regular in the starting line-up has come under pressure from Kieron Trippier.
Cardiff remain unhappy with Derby's decision to postpone Sunday's Sky Bet Championship game at Pride Park.
Dundee United boss Csaba Laszlo has been left hoping for St Mirren to slip up in the race to seal promotion to the Ladbrokes Premiership.
Crewe will consider starting Chris Dagnall when they host Forest Green on Tuesday.