Hugh McGinley, 52, is suing Miss Mone's firm MJM International for constructive dismissal and is asking for £20,000 compensation for loss of earnings.
Mr McGinley claims his workload increased substantially after his immediate boss, the finance director, left and was not replaced.
He told a tribunal in Glasgow that he was forced out of the job he had held at the company for six years because of stress and pressure.
Mr McGinley said the demands on him from Miss Mone increased at the end of 2012 when the company was in "serious financial difficulties".
The tribunal before judge Jane Garvie continues.