Extremely unlikely that the worn cam is the culprit, though if it's worn that much it couldn't hurt to replace it once you fix the real problem. You're losing a LOT of compression in that cylinder. You could have any number of problems that can only be ruled out through testing:
- Worn rings
- Worn valve(s) or valve seats
- Blown head gasket
- Cracked head
Have your mechanic check things out before you waste money on the cam (which probably won't help anyway...if it was the cam you'd be losing compression all over, not just markedly on one cylinder).
Cheers,