Are you sure that it is the clutch and not a broken belt or belt fallen off a pulley ?
Sit on the mower , ignition on engine not running and turn the blades on.
You should hear the PTO solenoid klunk .
IF not get under the mower and check the clutch.
Follow the wire from the clutch back to the connector
Check also that the clutch is still held by the retainer and has not jumped off .