The Pilgrims have been left without a manager since Paul Sturrock left for Southampton late this season.
Warnock joined the Blades in December 1999 when they were in trouble both on and off the field. The former Huddersfield man changed the team around and last season guided the Blades to Semi-Final of League and FA Cup only to lose to eventual winners Liverpool and Arsenal.
He also took the Bramall Lane club to Play-Off Final which Wolverhampton Wanderers won 3-0.