The Pilgrims will retain the 33-year-old's National League registration but the experienced campaigner could make his debut for the Gladiators at Basford United on Monday evening.
Westcarr made six appearances for the Pilgrims between August 11 and September 1, including five outings from the bench.
Harrogate Town defender Toby Lees, meanwhile, has returned to the CNG Stadium at the conclusion of his month-long loan spell with the Pilgrims. Lees (21) made five appearances for the Pilgrims and departs with the club's best wishes for the future.