Parkinson said: "Ideally, you'd always like to add to your squad and I'm no different from any other manager. But finances dictate.
"We'd like to sign our own players and if that's not possible, then the next option is the loan market. But I doubt there will be many more incoming."
Mooney's loan spell from Reading expires at the start of December, but after the striker scored his first goal for the club in last week's 5-1 win over MK Dons, Parkinson may attempt to extend his stay.
"It's something we'll address next week. The loan window ends but you can still extend existing loans," he added.