The eight-year-old was second to Teaforthree in the four-miler at the Cheltenham Festival last March and was last seen finishing ninth in the Hennessy behind Gold Cup favourite Bobs Worth.
The Manchester United manager owns Harry The Viking with three others, including Ged Mason, with whom he enjoyed great success with What A Friend.
Nicholls posted a picture on Twitter of Harry The Viking schooling at his Ditcheat stables, and said that Tidal Bay and Join Together will also be entered as he aims to follow up the success of Neptune Collonges last year.
"Harry The Viking (Daryl Jacob) schooling this morning. Will have entry in Grand National with Tidal Bay and Join Together," Nicholls said on Twitter.