Stephen Robinson has revealed Mark O'Hara will be sent for a scan on a thigh injury this week as he faces a month out of action.
The St Mirren captain was sidelined for the win over Dundee after picking up a knock in training.
And he is set to discover a diagnosis on the injury on Monday with a scan booked.
Robinson is hopeful the knock is nothing serious with a possible three to four week lay-off the positive early timeline for a return.
Robinson said: "It's a huge blow for us. It happened right at the last minute.
"We're getting a scan on Monday morning.
"We think it's short-term, between three and four weeks.
"It's a big blow but I thought the boys that came in took their chance.
"It's a thigh problem."
The St Mirren boss went on to offer his verdict on the reception for Joe Shaughnessy and Trevor Carson on their return to St Mirren for Dundee.
The duo received mixed reactions from the home crowd with Shaughnessy receiving warm applause and Carson booed after his exit in the summer.
The pair would also combine to gift an early lead to the hosts as Shaughnessy turned into his own net from a Conor McMenamin cross.
Robinson explained: "Football is pantomime. Some of the things that get shouted at me, I think surely they don't mean that. Maybe they do!
"I've had a brilliant relationship with Trevor for a long, long time. I class Trevor as a friend and I wish him nothing but success.
"Dundee have got a very good goalkeeper there.
“I only realised it was him that scored the OG but listen Joe was excellent for me in the year we were here together.
"He was a very good servant to the football club before that so I have nothing but best wishes for him and Trevor."
