Wigglesworth had enjoyed a fine individual World Cup with England and, with Ben Youngs' own knee problems, had been looking to stake a significant claim for the No9 shirt in next year's RBS 6 Nations.
But instead of looking forward to further enhancing his reputation in 2011, the former Sale star will be sidelined for the next seven to nine months.
"Richard injured his knee in Sunday's game so he's had his ACL reconstructed and will miss the rest of the season," said Saracens' director of rugby Mark McCall.
"It's a massive blow for Richard. He's been phenomenal since he arrived at the Club and has gone from really being nowhere to getting himself into the English World Cup squad. He had a great World Cup and was one of their standout players for me.
"To have injured himself in the way he did in his first 10 minutes back with us is a massive individual blow because I'm sure he would have been involved in the Six Nations.
"Unfortunately these things happen. It's the first injury he's ever had, the longest he's been out is two weeks so we feel desperate for him, but we know he'll bounce back."
Experienced South African Neil de Kock will fill the void left at scrum-half by Wigglesworth's absence, with the emergence of a promising young No9 ensuring Sarries won't be looking to buy a ready-made replacement.
"It's a big blow to us as well. But we're lucky in that we've found an 18-year-old in Ben Spencer from Cambridge who's almost a mini Richard," added McCall.
"We're certain he'll play for England Under 20s this year so we're not looking to recruit."