Birmingham will make 20 percent of the fee Stoke receive for Butland as part of a sell-on clause written into the deal that saw the England international move to the Bet365 Stadium from St Andrew's in January 2013.
According to Sky Sports, the Potters value the 25-year-old at £30m and Chelsea are seriously considering the stopper with rumours Thibaut Courtois is set to join Real Madrid.
The Blues previously wanted Butland's international teammate Jordan Pickford to replace Courtois, but have been forced to look elsewhere with Everton refusing to negotiate.
Informal contact has been made between the two clubs at boardroom level, but Stoke want any potential deal sorted out quickly so that can find a replacement themselves.
With Birmingham having been given transfer sanctions by the EFL this summer as part of Financial Fair Play rules, money from the sale of Butland would be an extremely welcome cash windfall.