Kelvin Wilson and Charlie Mulgrew both missed their team's disappointing 2-1 loss to SPL rivals Motherwell at Fir Park on Wednesday.
However, centre-half Wilson, who was ruled out of the game with a migraine, and utility man Mulgrew, who had a glute problem, could be back this weekend.
The duo's availability will increase the Parkhead club's hopes of beating Saints in Paisley and booking a semi-final date at Hampden.
Celtic manager Neil Lennon said: "Kelvin will be back in the squad for the weekend. He had a migraine the other evening and missed the Motherwell game.
"And we are hoping that Mulgrew, who has missed our last couple of matches, will be fit too.
"Apart from those three, our long-term absentees, Scott Brown and Mikael Lustig, should still be missing."
Meanwhile, Lennon has admitted he is hoping to see a reaction to the Motherwell loss when his team take on the Buddies in the last eight of the Scottish Cup tomorrow.
Saints dealt his team one of the most painful defeats of the 2012/13 campaign when they won the League Cup semi-final 3-2 at Hampden last month.
Lennon was scathing about the application and performances of his players in the midweek SPL defeat to Stuart McCall's team.
And he publicly threatened to axe the players responsible if there was a repeat of the no-show in a game that will be screened live by Sky Sports.
He said: "I would hope and imagine I would get a positive reaction to the Motherwell defeat on Wednesday night when we play against St Mirren.
"I had to rotate the squad the other night. It was the start of a run of three games in seven days and we had some big games coming up.
"We have St Mirren in the Scottish Cup tomorrow and Juventus in the Champions League on the horizon. I felt I was justified in making the changes because of that.
"We took a hit the other night. I have to look at my own selection and ask myself whether the team was strong enough.
"I certainly thought it was before the match. But did we perform well enough on the night? No, we didn't. Hopefully our performance will be far better this weekend."
Meanwhile, Rami Gershon has just started training again so he should also be fit.