Greg Halford has been backed to help remedy Pompey's defence after sealing his return to the club.
The Blues have been boosted by Halford agreeing a new loan stay from Wolves until the end of the season.
The 26-year-old inked a new agreement last week to boost Cotterill's options.
Pompey looked to be on their way to a hard-earned clean sheet at Nottingham Forest on Saturday. But two late goals took the total to 14 goals shipped in the past five games.
Cotterill was left frustrated by that in the wake of the agonising defeat.
Aaron Mokoena's booking also means he will serve a two-game ban Pompey can scarcely afford.
Nadir Ciftci is struggling with an ankle problem, John Utaka limped off at Forest with a hamstring injury and Ricardo Rocha is still not fit.
Cotterill is pleased to have Halford back, however – although he warned him there can be no repeat of the red card at Watford which kept him out for three games.
The Pompey boss feels he can offer much-needed help for his side now on the back foot – and also going in the other direction.
Cotterill said: 'Greg blotted his copy book a bit with his red card, but players are human and make mistakes.
'We paid for that when he was out, but we have to look at it as a whole and ask has he been good for us?
'The answer to that is "yes", so that's why we got him back. He's been a goalscoring right-back for us and there's not too many of them around.
'We're pleased he's back and training with us. It's good to have him here again.'