Mallow teenager Liam Lynch, who requires the motorised wheelchair, has been in hospital since January 19 and has missed his mock Junior Certificate examinations as a result.
The HSE said funding restrictions mean it cannot process all applications for powerchairs immediately.
Liam has needed a wheelchair since the age of seven when he was diagnosed with a tumour in his spine and scoliosis.
His mum has been appealing for a new powerchair, to accommodate his growth, for more than six months.
“He’s had a powerchair for the past four or five years and he’s outgrown it,” said his mother, Grainne Lynch.
“Liam needs a special moulded seat and his occupational therapist recently said it needs a moulded back because of his scoliosis.
“We’ve been waiting months for a new chair and as a consequence, Liam has suffered stage four pressure sores,” she added.
A stage four pressure sore can cause extensive damage as it reaches into muscle and bones on occasion.
Mum Gráinne added: “It’s so frustrating, he has to have surgery next week, all because he couldn’t get a new chair, because his case wasn’t deemed urgent enough.