The central defender returned to action when replacing the ill Brett Solkhon at half-time during last weekend’s 3-2 defeat at Weymouth.
Malone has been working his way back to fitness after undergoing a gall bladder operation.
But Law confirmed he broke down ahead of the 3-0 midweek defeat at Leamington, adding further problems to the centre-half position.
“Paul won’t play again this season,” the Poppies boss said.
“He broke down in the warm up to the game on Tuesday and I think there was a realisation last weekend that he is not as far ahead as he thought he was.
“It is a mixture of his knee and the operation he had, it is a combination of both. It’s a real shame and we are really struggling in that department at the moment.
“Brett had some problems with sickness at Weymouth and wasn’t 100 per cent fit on Tuesday but still went on and did a shift off the bench.
“And Dom (Langdon) was struggling with a bit of an ankle knock as well so it left us a bit short.”
There may, however, be good news on the horizon over the fitness of James Haran who has been missing for a number of weeks due to a groin injury.
“James is due to train tonight (Thursday) and we will see how he goes,” Law added.
“He took part in a vigorous warm-up on Tuesday and we are hopeful he isn’t far away.”
The Poppies take on St Ives Town in the Evo-Stik Southern League Premier Division on Saturday before hosting Brackley Town in the NFA HillierSenior Cup semi-final on Tuesday night.