It is understood that the Celsis board turned down a cash bid for Celsis Laboratory Group, its US division, from Arthur Holden, who resigned as chief executive last month, because the price offered was too low.
CLG, which owns two laboratories in St Louis, Missouri, and New Jersey, accounted for around a quarter of Celsis's pounds 16.2m turnover last year.
At the time of his resignation, Mr Holden, who now lives in Chicago, had said that he was looking at making a bid for the whole company or taking it private.
However, yesterday's setback appeared to signal the end of Mr Holden's ambitions to own Celsis, as the company said that he did not intend to make an offer for the whole group and all discussions with him had terminated.
In a separate development, Celsis said that a "number of other parties had expressed an interest" in opening talks over a possible takeover.
The finance director, Mark Harris, said that it had been approached by about four other companies.
Mr Harris declined to name the potential bidders but said that they were "leading companies in the field" and were all "substantially bigger than Celsis".
Celsis said it was "reviewing" the approaches but added that it is "not seeking a purchaser".