Scott Kilday made the accusation at an employment tribunal where he is claiming unfair dismissal against Miss Mone's MJM International firm.
The 35-year-old also said his relationship with Miss Mone had latterly become "tense".
Mr Kilday, an operations director who left the firm after discovering his office had been bugged, was giving evidence for a second day at the hearing in Glasgow.
The hearing was told how problems had arisen in the company after Miss Mone split with her husband and business partner Michael in December 2011.
Mr Kilday said: "Michelle is a very difficult person to work with." Mr Kilday now works for Michael Mone's Pendulum Apparel firm.