This month, the team from the University of Leicester started a fresh excavation at the site. Now in their final week of digging, the researchers plan to open the coffin in the days ahead.
They think it might contain the remains of the knight Sir William de Moton of Peckleton, who died between 1356 and 1362, or one of two heads of the Grey Friars order in England, Peter Swynsfeld or William of Nottingham.
"Stone coffins are unusual in Leicester - and this is the first time we have found a fully intact stone coffin during all our excavations of medieval sites in the city," site director Mathew Morris, of the University of Leicester Archaeological Services (ULAS), said in a statement. "I am excited that it appears to be intact.
Morris and his team intend to measure and take photos of the coffin before they lift the lid, which they say they will do out of view of the media.
Meanwhile, Richard's remains are set to be reinterred next year. Last week, the Leicester Cathedral announced its $1.5 million (£1 million) plans to rebury the king in a new raised tomb at the church.