One of the largest backers of ASX-listed software and services company Citadel Group says a $503 million acquisition bid by private equity outfit Pacific Equity Partners is disappointing, despite it coming at a 43.2 per cent premium to its previous closing price.

Carlos Gil, the chief executive of Microequities Asset Management, which is Citadel's fourth largest backer with a 6.4 per cent stake, said he believed the bid was opportunistically timed, before a company turnaround strategy could bear fruit.