"I saw him play during his time at Yeovil, he did well for them and played his part in a good run for the team," said Northampton manager Stuart Gray.
"He's been training with us this week and I'm sure he'll fit in well."
Gray added: "We are very grateful to Nigel Clough at Derby for allowing us to borrow Aleksandar," said Gray.
"We saw Andy Todd benefit from a loan spell with us earlier in the season, and hopefully Aleksandar will be good for us and we will be good for him."
Prijovic is expected to be in the Cobblers' squad for Saturday's visit of Stockport County in League One.