The Wembley showpiece for the 2019-20 season will finally take place almost a year later than scheduled amid the coronavirus pandemic.
The clash will also take place behind closed doors, despite the Blues selling more than 50,000 tickets for the original date 12 months ago.
Both sides are currently locked in a heated promotion battle in their respective divisions.
Salford meanwhile, are pushing for a League Two play-off place and sit ninth in the table.
Wellens admits he'd rather the final take place after the league season was completed as it's a ‘distraction’ to the Ammies' main priority.
The former Swindon boss told BBC Radio Manchester: ‘The league is the priority. If anything, this game is a distraction,
‘There are no supporters there. I've played at Wembley in front of 80,000 so it's not going to do anything for me. It's a bit of a hindrance but, for the players, it will be a huge honour and we'll treat it very seriously.
‘It just means with that game being on a Saturday, we've had a postponement to a league game and that's another extra Tuesday game.
‘I don't know why the powers that be couldn't organise it to be after the last game of the season because our schedule is already taken up.’
Pompey take on Salford for the first time in the club’s history.