Kenny Jackett is weighing up employing a back three as Pompey strive to swiftly respond to their Gillingham set-back.
The table-topping Blues suffered a maiden defeat of the League One season last weekend, falling to a 2-0 Fratton Park loss.
They head to AFC Wimbledon on Saturday, deprived of Ronan Curtis through international duty and injured pair Andre Green and David Wheeler.
Jackett admitted their absences from his attacking left-sided options has forced him to consider a system switch.
The Blues boss experimented with a back three during the second half of Tuesday night’s Checkatrade Trophy win at Crawley.
That saw Matt Clarke, Christian Burgess and Anton Walkes operate as the central defenders.
And Jackett concedes it’s a game plan which may be rolled out again.
He said: ‘That system is something we have been close to on one or two occasions, so I wanted to experiment in the second half (at Crawley).
‘It can either get us back into a game if we are behind or, in a tight match, to pose the opposition a different type of problem.
‘It’s an option we need to look at – and Tuesday night was the right time to
experiment with it.
‘It has to be right in terms of balance of the team, the right players at the right time and how we stand at the minute with injuries.
‘We’ll see if it’s used again. Green is out injured, Wheeler is out injured, Ronan Curtis is away, so if you are in that situation you consider it. We feel we have some good attacking full-backs as well.
‘How it did against Crawley was interesting, there were some good things, there were also times when we didn’t quite get it right, but we are learning.
‘That’s the reason for experimenting in a game like that, so when we play the league games we can get it right.’
Jackett’s formation change at the Broadfield Stadium also saw Brandon Haunstrup and Haji Mnoga initially operate as wing-backs.
The substitution of Mnoga for Tom Naylor prompted a reshuffle, with the latter dropping into the back three and Walkes moving to right wing-back.
It was from that role that Walkes won an 88th-minute penalty, which Joe Mason subsequently missed.
The versatility of the former Spurs man continues to be a prized asset in Pompey’s squad.
Jackett added: ‘I think Anton is comfortable enough to do a job across the back four.
‘Although I do see him predominantly as a right-back.’