Walton Casuals have announced a pre-season clash with Pompey.
The Ryman League south division outfit have revealed that the Blues will travel to Surrey to face them on Saturday, July 27 (3pm).
Pompey have yet to confirm the fixture but a squad of development and Academy players will be expected to make up their team on the day.
Walton were relegated from their league last season but were handed a reprieve by the Football Association after a reallocation of sides into the non-league pyramid for the new campaign.
It means they play four levels below Guy Whittingham’s men.
There is a connection between Pompey and the Stags, with the Blues’ former head of recruitment Luke Dowling an ex-manager of Walton.
The friendly will take place 24 hours before the Blues take on La Liga outfit Rayo Vallecano in a testing final warm-up game at Fratton Park ahead of the start of their League Two campaign at home to Oxford on August 3.
Pre-season training begins in earnest for Pompey’s players on Monday after two days of fitness testing finishes today.
Their friendlies begin with a trip to Westleigh Park to take on the Hawks on Tuesday, July 9, before Whittingham’s men go to Nyewood Lane to play Bognor on Saturday, July 13.
The team depart for a week-long training camp in Colchester with a match at Blue Square Bet Premier outfit Braintree on Tuesday, July 16.
Pompey return from Essex to take on Charlton at Fratton Park on Saturday, July 20 before travelling to Dean Court on Tuesday, July 23 to take on newly-promoted Championship outfit Bournemouth.
Walton Casuals will be next up ahead of the game with Rayo Vallecano, who last season finished eighth in the Spanish top-flight.
A development squad match with Gosport Borough is earmarked for Tuesday, July 30.