Birmingham have turned down a £6m bid from Saints for goalkeeper Jack Butland, according to reports.
The 19-year-old, who was a part of England's squad at Euro 2012, is in high demand this summer.
Birmingham's acting chairman Peter Pannu said this week that the Championship club would only sell their young keeper for "eye-popping" money.
Saints appear to have now tested that resolve, but without success.
Butland is yet to play for the Blues, having made 24 appearances on loan at League Two side Cheltenham last season.
However, new manager Lee Clark expects him to become the replacement for Ben Foster, who is expected to leave St Andrew's for West Brom.
Clark said: "Jack wants to come in and be number one and that's what we see him as."
He added: "He's got a huge part to play in the future of this club."