Francis, 57, who was Britain’s first £1 million footballer, was taken ill on Friday and is recovering in Birmingham Heartlands Hospital.
A spokesman for Birmingham, an npower Championship club wished him a “speedy recovery”.
A statement on its website said: “Everybody at Birmingham City FC would like to send our best wishes to club legend Trevor Francis following news that he is recovering from a suspected heart attack.
“The former Blues striker and manager is much loved by everybody associated with the club and we’d like to wish Trevor a speedy recovery.”
Francis played for the Blues between 1971 and 1979 before becoming Britain’s first £1m player when he joined Nottingham Forest.
He went on to play for Manchester City, Sampdoria, Atalanta and Rangers.
He also managed Birmingham between 1996 and 2001.