Kenny Jackett conceded Pompey’s preparations for Gillingham were bundled off track following Oli Hawkins’ injury.
The striker collected a hamstring strain on Friday while warming-up in training.
That did, though, prompt a change in system and personnelKenny Jackett
Hawkins had been set to start against the Gills in a system which included Jack Whatmough in the centre of midfield.
His absence prompted a reshuffle, with the Blues instead lining-up in a 3-5-2 formation, with Kal Naismith and Jamal Lowe in attack.
And in Hawkins’ absence, Jackett’s men suffered a 3-1 loss, influenced by a second-half collapse.
Pompey’s boss said: ‘Oli was injured on Friday in training.
‘These things happen, the focus is always on the players that are fit and here, not the ones that are not.
‘That did, though, prompt a change in system and personnel. Regardless, it did give us a good foothold in the first half, I don’t think it gave us too many problems.
‘You have to be able to change personnel and systems as part of a league season and while there is frustration at every injury, it becomes about the players that you have.
‘We worked hard all week and Oli felt it doing some warming-up work. I would think he is out for 2-3 weeks.
‘In terms of hamstrings, it’s not a bad one, but even a minor one can take a little bit of time and I think probably this one will.’
Irrespective of Whatmough’s positional change, Saturday marked his first appearance in more than six months.
The Gosport youngster damaged knee ligaments against Rotherham in September, but battled back to return against Gillingham.
He operated on the right of a back three containing Matt Clarke and Christian Burgess.
It was an appearance which spanned 76 minutes before making way for Conor Chaplin – and Jackett was pleased with Whatmough’s contribution against the Gills.
He added: ‘I have a lot of time for Jack, he started the season well for us.
‘Saturday was his first game back from injury. I thought he was solid and will get a build on that.
‘I am pleased to have him back and pleased for him personally because he has worked hard.
‘Jack is centre-back and I felt in terms of the set-up of the game, in the first-half everybody bar Jamal was in their natural position. Jamal also did well and was a threat for us throughout.
‘In terms of Jack, he is a defender and we look at different scenarios in training.’
– NEIL ALLEN