The Blues captain is facing up to a lengthy period out after picking up a training-ground injury to his thigh, which has ruled him out of the past three games.
It’s a sizeable blow to Cowley’s plans after Robertson’s impressive start to the season, following his summer arrival after leaving Rotherham.
His absence has seen the Blues head coach go to a back three in the past two games and springing a surprise, as he utilised Kieron Freeman and Shaun Williams either side of Sean Raggett.
There’s been clear benefits to that move across the pitch, but games against Plymouth and yesterday’s 2-2 draw at Charlton Athletic have also seen individual defensive errors prove costly.
That restricted him to 16 Championship appearances last season and 22 outings the previous term.
The Pompey head coach also reckons there was no way an injury of the nature Robertson suffered could’ve been anticipated through what has gone before.
Cowley said: ‘We really felt the pain for Clark, we knew he was desperately disappointed.
‘The injuries he had at Rotherham were linked to his metatarsal, a bone in his foot.
‘To be fair, he broke it, he thought it had healed and they talked at the time about operating on it.
‘They decided not to, he came back, it got trodden on and it broke it again. Then they operated.
‘So that was a very different injury to the one he’s now sustained.
‘Sometimes these things happen in football and it’s frustrating for us all – but that’s where we’re at.’
A message from the Editor, Mark Waldron
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