New West Ham owner Sullivan has intimated that he is interested in luring both of his former players to Upton Park at the end of the season by trying to take advantage of a perceived loophole in their contract situation at St Andrews.
The contracts of Larsson and Ridgewell expire at the end of the current season, with Birmingham holding a further 12-month option on both players.
But Sullivan, who negotiated both deals while still chairman at Birmingham believes the option clause may not be permissible under Fifa regulations, if written confirmation of taking up the option is not submitted to both players before a stipulated date.
Bitter battle looming: Alex McLeish (left) has challenged David Sullivan
The irony of Sullivan putting together the deals he is now trying to exploit is not lost on McLeish, but he has made it clear the clubs new owners will not just roll over and allow two of their assets to walk West Ham.
'This in the man that did the contracts in the first place. They used them year-in, year-out at Birmingham,' said McLeish.
'I don't know why they thing they are no recognised by FIFA, but if someone wants to challenge it it will be four or five years before it is resolved.
'There will be lawyers and all kinds of paper work. It is not going to be ratified in 24 hours after one call to FIFA.
'Our contracts are approved by the Premier League and for someone to challenge them it would be a protracted and drawn out affair. So they are welcome to try.'
In demand: Sebastian Larsson (right)
Swede Larsson is looking for a significant increase on his £8,000-a-week deal, after turning down opportunities to leave the club over 12 months ago.
Ridgewell wants to see his £12,000-a-week deal given a major hike to reflect the part he has played in Birmingham's success this season.
But McLeish, who is also in the process of negotiation over a new contract for himself, wants all contract issues to be left until the end of the season.
'We have to keep driving people on and I am in no rush to have to deal with things like contracts. We don't want to discuss anything until the end of the season.' McLeish enters talks over new Birmingham deal with owner YeungWest Ham confirm Davenport has left after defender accepts £250k pay-offBIRMINGHAM CITY FC