His role in the movie is currently unspecified.. Deadline has stated that this is a lead role and will be apart of future Marvel movies.
With most of the leads already cast, it is rumored that Del Toro may be playing the role of THANOS, the Mad Titan. Del Toro will be joining other cast members Glenn Close (unnamed role associated with the Nova Corps), Michael Rooker (Yondu) Dave Bautista (Drax the Destroyer), Chris Pratt (Star Lord), Zoe Saldana (Gamora), John C. Reilly (as a member of the Nova Corps), Lee Pace and Karen Gillian (unspecified roles).
Guardians of the Galaxy, written and direct by James Gunn is scheduled for release on August 1st 2014.
Stay tuned to Fanboys Anonymous for more news on Marvel Phase II.