Former Blues midfielderCarsley was the Sky Bet Championship side’s assistant manager underSteve Cotterill, who was sacked on Saturday.
And with new bossGarry Monk namingPep Clotet as his assistant,Carsley has departedSt Andrew’s.
Carsley had previously taken caretaker charge of Birmingham followingHarry Redknapp’s exit last year.
Southampton remain in the hunt for Red Bull Salzburg's Amadou Haidara and are reportedly readying a £15million offer.
Aston Villa are reportedly weighing up a summer move for out-of-favour Huddersfield defender Michael Hefele.
Southampton are lining up a summer bid for Huddersfield Town midfielder Aaron Mooy, reports claim.