A person attending the Tuesday meeting said that YSL chief Paul Deneve made the announcement to personnel.
Rumours have been rampant that Slimane would replace designer Stefano Pilati who joined the house in 2004 — and presented his final YSL collection on Monday.
The YSL employee says that Deneve didn't say when Slimane would start his new job. Slimane is a former Dior Homme designer.
The employee was not authorized to speak publicly about the appointment and spoke on condition of anonymity. Phone calls to YSL went unanswered.
The employee says personnel were told that an announcement would be made on Wednesday.