The 34-year-old Spaniard has moved to the Sky Bet League 1 side until the end of the season, subject to international clearance, after a four-month spell at Morton came to end in January.
But Riordan, the former Celtic and Hibernian striker, will not be joining him at Brunton Park after manager Graham Kavanagh lost interest when the 31-year-old failed to report for training last week.
Kavanagh, however, is delighted to land Novo and hopes to hand him an immediate debut in Saturday's trip to Crawley. "It's about getting his clearance now," he said.
"He gives us a know-how and knowledge and composure that I hope will rub off on the other players and excite the fans."