Ritchie hobbled off during Wednesday night’s Carabao Cup defeat to Leicester City after a horror tackle by Hamza Choudhury.
And Bruce has confirmed the Scotland international – an integral figure in the United starting XI – will likely miss eight weeks of football with bone bruising, stitches and ankle ligament damage.
“It's not great news. We think he's going to be maybe two months, eight weeks,” said Bruce.
“There is ankle ligament damage too, bone bruising, cuts. The kid, as I said to you the other night, was a mess.
“Thankfully it's not six months, but it's bad enough when it's the best part of eight weeks.”
On Saint-Maximin’s hamstring problem, the news is a little better.
“It's a grade 1, so we think it's going to be anywhere between three weeks and five,” said Bruce.