Paul Cook admitted he feared the worst for Jack Whatmough after his injury setback.
But Pompey are confident the defender will be back playing inside three months.
Whatmough is focusing on another knee-injury battle, after hobbling off in last weekend’s 0-0 draw at Crewe Alexandra.
The good news for the 19-year-old, however, is it isn’t a recurrence of the issue which left him sidelined for 10 months last year.
Cook spoke of his frustration for the defender who was dealt the setback after starting the season in the middle of defence.
The Crewe clash was just Whatmough’s third competitive start for the Blues after battling back from his previous issue.
Cook was relieved to see the Gosport talent avoid the same problem picked up against Cheltenham.
But he tempered that with the fact he knows Whatmough is facing another dose of disappointment.
Cook said: ‘It’s nothing to do with the last injury, which is great news for Jack.
‘It’s still not a nice injury for him, though, at all.
‘But it’s not really a bad one in terms of cruciates.
‘Everyone feared the worst. Of course we did.
‘It’s disappointing for Jack because he’d had a good start and looked commanding.
‘He was finding his feet well and now he’s had this new setback.
‘He’s a young lad and he’s having to deal with a lot of disappointment.
‘We hope he can get back as soon as possible – and he’ll have our full backing in doing that.’
Whatmough underwent a scan on Monday after leaving Crewe on crutches and in a knee brace.
The result of that showed it was not a repeat of the previous anterior cruciate ligament he had in his left knee.
Whatmough has suffered damage to his medial collateral and lateral collateral ligaments, however.
That means he is expected to be in a knee brace moving forward as he begins the rehab from the problem.
First-team coach Ian Foster outlined the details of the injury and the timeframe Whatmough will be working to.
Foster said: ‘He’s hurt his MCL and LCL. It was his ACL last time.
‘So that means he is going to be in a knee brace for six to eight weeks.
‘He will be doing his rehab during that but we are probably looking at 10 to 12 weeks.’
– JORDAN CROSS