A host of Premier League sides have been linked with Butland during the transfer window, including Liverpool and Arsenal, but the player's agent Gary Mellor has confirmed that Chelsea are the only club to have a concrete offer accepted.
Mellor told The Sun: "Chelsea have been given permission to speak to Jack.
"At this moment they are the only club who have registered a bid."
Birmingham's entire first-team squad is on the transfer list due to financial strife, leaving Blues CEO Peter Pannu will little choice but to accept Chelsea's bid.
Butland will now travel to London this week to discuss personal terms with Chelsea ahead of a proposed move.