Birmingham have been one of the most active sides in the transfer market so far this summer but McLeish remains adamant his squad needs further reinforcements before it is ready for the new season.
Top of his priorities list is strengthening the midfield and Sullivan claims there are a number of different players under consideration.
"We are looking to strengthen the team further and, for a midfielder, we've got eight balls in the air at the moment," the Blues co-owner told the Birmingham Mail.
"We are working hard and hopefully one or two things will be resolved in the coming days."
McLeish completed the free-transfer capture of Lee Bowyer last week but the Scotsman is keen to add a different option, with Patrick Vieira still being linked with a move to St Andrews'.
"We need a different type of player in the midfield because we have got players who are of similar style," said McLeish.
"Lee Carsley and Damien Johnson have got their own fantastic qualities, Keith Fahey is different from them even.
"But I feel we still need some other players to augment the talents of Carsley and Johnson, and now Bowyer."