Nottingham University was accused last week of "vindictiveness" for its pursuit of IVF pioneer Simon Fishel through a bitter High Court trial.
The university is suing Dr Fishel for Pounds 400,000, claiming he was running a private practice while a full-time employee.
Dr Fishel has been accused in court of using "actual deceit" to cover up his business dealings.
But Dr Fishel, who was scientific director of the university's IVF unit until July 1997, vehemently denies making "secret profits". His lawyers say he in no way breached his employment contracts.
In his closing submission Ashley Underwood, for Dr Fishel, accused the university of "vindictiveness and self-justification".
He also said: "Despite the oddly mean-spirited attempts to devalue his work, it is clear that the university benefited from that research."
But Tim Dutton QC, the university's counsel, said: "When one asks the question 'has he breached the duty of fidelity he owed to the university?' the answer is not hard to arrive at."
By receiving payment for treatment runs to Rome, Cairo, Saudi Arabia, South Africa, Greece and Sicily, Dr Fishel was "simultaneously serving two masters".
Mr Dutton said Dr Fishel had known since April 1993 at the latest that there were procedures for seeking permission for outside work.
Mr Justice Elias will give his judgment at a later date.