The Scot walked out on Sunday and was immediately linked with a controversial move across the city to Aston Villa.
Villa, looking to replace Gerard Houllier, are huge admirers of McLeish, 52, and are understood to be considering him now he appears available.
McLeish's decision to quit by email - with two years left on his contract - has stunned Birmingham and left acting chairman Peter Pannu furious.
Legal battle: Birmingham will refuse to allow Alex McLeish to talk to other clubs
'I will be meeting my legal team tomorrow (Monday),' said Pannu, who was in Amsterdam tying up his club's fourth signing of the summer when McLeish's notice dropped into his in-box.
'Rest assured I will leave no stone unturned. It's about time some discipline is instilled into this game - and I am not a person who gets pushed about.
'We spent ?40million, supported him all the way, and what we get is a relegation and a snub when the owner gave him unwavering support and did not sack him, and declared his job secure and professed trust and confidence in him.
'We just bought him three players of his choice and I've been in Amsterdam securing him a fourth. Then I get an email while I'm on business and that speaks volumes.'
Pannu insists Villa have made no official approach and McLeish, who has been on holiday, will not be allowed to talk to anyone.
Furious: Peter Pannu (third right) with the Birmingham City board
Pannu added: 'I won't blame any outside clubs yet until I find out more. He is still our contracted staff and Birmingham City does not grant him any right to speak to any outsiders until the matter is resolved.'
McLeish, who led Birmingham to Carling Cup triumph - their first silverware for 48 years - against Arsenal last season, has been at loggerheads with Pannu and owner Carson Yeung over the last few months.
However, Yeung has sanctioned the recent signings of disgraced striker Marlon King plus winger Chris Burke, Morgaro Gomis and Dutch striker Danny Koevermans.
Now McLeish has taken the ultimate gamble by walking out. Birmingham could put him on gardening leave or demand a huge compensation package.
McLeish is also taking a risk with Villa but owner Randy Lerner is a fan and admires the job that the Scot has done at the Second City's other club. He fits the bill in that he has a proven Premier League pedigree.
Ironically, Villa had already been linked with Birmingham pair goalkeeper Ben Foster and defender Roger Johnson.
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?Explore more:People: Marlon King, Alex McLeish, Gerard Houllier, Roger Johnson, Ben Foster Places: Amsterdam, Birmingham
Source: Daily Mail
Source: Daily Mail