Argyle currently have a four-point cushion between themselves and the npower League Two relegation zone and another three points would secure fourth tier football for another season.
But they will have to manage without Swindon loanee Cox who will not play again this season after tearing shoulder ligaments.
The former Leicester trainee suffered the injury in Argyle's 1-0 win over Exeter on March 30, his 10th appearance for the Pilgrims, and has been sidelined since.
Striker Warren Feeney will miss out once more having been sidelined since January.
The Pilgrims head into this clash full of confidence having won five of their last seven games.