He is a member of the security staff at the four-star Legends Hotel, police on the island confirmed.
On Monday, about 3,000 people attended the funeral of the teacher, 27, who was strangled a week ago on her honeymoon.
A spokesman for police in Mauritius confirmed a further person is in custody in connection with the murder.
He told the BBC: “He is one of the persons who was engaged in security work.”
Three men, all staff at the luxury hotel, have been charged in connection with the killing, thought to have happened as newlywed Michaela disturbed a burglary in her room.
Room attendant Avinash Treebhoowoon, 29, and floor supervisor Sandip Moneea, 41, have been charged with murder, and room attendant Raj Theekoy, 33, with conspiracy to murder.
They are due to appear in court today.
Michaela, from near Ballygawley, Co Tyrone, was the daughter of Tyrone GAA manager Mickey Harte. On Sunday, her father and husband John carried her coffin as the crowd walked in silence to the church where she was married to John just last month.
She was buried in her wedding dress.
President Mary McAleese was among dignitaries at Requiem Mass.
Bishop of Dromore John McAreavey, the widower’s uncle, married the couple and delivered the address.
Mr Harte, Michaela’s mother Marian, and brothers Mark, Michael and Mattie led mourners at the compact country church after one of the main roads running through Tyrone was closed for the funeral procession.
Symbols representing Michaela’s beauty, faith, love of family and the Irish language were presented at the beginning of the service.
All-Ireland Primate Sean Brady also took part.