The former Chelsea striker is in demand after scoring for fun in League One, and the Robins are under pressure to sell should they not gain promotion to the Championship.
Parkin had a loan spell at Millwall, where he showed plenty of potential - scoring 4 goals in 5 starts.
The deal was not made permanent, as Chelsea's £1m price tag was deemed too high by the Lions.
The burly forward was later loaned out to Wycombe, Oldham and Northampton before signing for Swindon in 2002.