Pritchard spent time on loan at Posh from Tottenham last season and the club had hoped to bring the 20-year-old winger back to London Road for a second temporary spell.
However, after contacting Spurs MacAnthony insists he has been told the player is poised for a move to Wiltshire.
"We want him and the boy wants to come to us," MacAnthony said on Twitter. "Spurs insisting he goes to Swindon. Nothing we can do I'm afraid."
An injury-interrupted spell at Peterborough saw Pritchard make six appearances for Posh last season, starting the final two games of the season, after joining the club in January.