A slipping clutch? Through low fluid/knackered cylinder?
Think again... the hydraulics are used to push the fork which pushed the bearing which acts on the centre of the cover which pushes the levers of the spinning cover in and releases the pressure on the plate - no more drive.
If it's slipping it's worn, or the cover is not exerting enough pressure on the plate anymore, or there is oil contamination on the clutch.