Martyn is hoping to raise around £2,000 for a fund set up to help his friend, in an internet auction ending at 1945 GMT on the 15th of January.
Martyn and Prescott played together in the Saints side that lifted the cup in 1996, having beaten Bradford Bulls 40-32 at Wembley.
"It's absolutely brilliant. To have won a medal like this, at Wembley, and to sell it to help somebody else is phenomenal," said Prescott's father Eric.
"Everyone, past and present players, have been fantastic. Tommy has been round to see Steve and we can't thank him enough."