The deceased former chief executive of CI╔ suffered health problems because of the stress of continuous media reports, the rail signalling inquiry heard.
Mr Bill McCamley, a bus driver and worker-director on the board of CI╔, told the inquiry that the late Mr Michael McDonnell was badly affected by repeated leaks to newspapers.
Mr McCamley said a series of articles in the Sunday Business Post appeared to be designed to humiliate or discredit Mr McDonnell and his policies.
The issue was an ever-present concern for Mr McDonnell and was discussed among his colleagues at board level.
"We waited in expectation for the next Sunday Business Post to see what next was going to be said. It certainly had an awful effect on Mr McDonnell's health. We could see the deterioration in him. It was fascinating in a cruel sort of way," said Mr McCamley.
At one stage, said Mr McCamley, Mr McDonnell had written to a consultant, Mr John Behan, who was then advising on the restructuring of the company, and accused him of leaking a document to the newspaper.
Mr McCamley found a copy of the letter while preparing for the inquiry but he did not know whether Mr Behan had denied the allegation.
Mr McDonnell's widow, Mrs Noreen McDonnell, wept during the evidence. Her husband resigned from CI╔ in February this year and died in tragic circumstances in April.
Mr McCamley said Mr McDonnell also had a difficult relationship with the Minister for Public Enterprise, Ms O'Rourke, whose policies were "diametrically opposed" to his.
"I would have thought the dogs in the street would have known that," he said under cross-examination.
Mr McDonnell's policy was for what he called a "socially integrated public transport system" which involved maintaining CI╔ as a single company, while the Minister's stated aim was to separate the city bus, intercity bus and rail components.
"Mr McDonnell believed that with all its flaws and weaknesses, real and imaginary, CI╔ had essentially sound foundations on which to build an integrated transport system," said Mr McCamley.
He had been determined in pursuing this policy and many stories had circulated about the difficulties this caused between himself and Ms O'Rourke.
Mr McCamley cited the example of the publication of a major rail safety review in late 1998. Ms O'Rourke had apparently called both Mr McDonnell and then CI╔ chairman, Mr Brian Joyce, to her office to discuss it but left Mr McDonnell standing outside the door.
The account was later contradicted by Mr Pat Mangan, assistant secretary at the Department of Public Enterprise, who said a misunderstanding had arisen as the Minister had only invited Mr Joyce in the first place.
On Tuesday, the inquiry heard evidence from Mr Joyce who also complained about media leaks and said a report in The Irish Times, which he attributed to a leak, was the immediate cause of his resignation in March 2000.
The inquiry is investigating a £36 million overrun in a new rail signalling system which ran into serious difficulties while Mr McDonnell was chief executive. The system, known as mini-CTC, is needed to improve safety and efficiency on the tracks but it is now two years overdue, is still unfinished and its cost has risen from £14 million to around £50 million.