The Irish prevailed despite injuries to O'Connell, first five-eighth Johnny Sexton and flanker Peter O'Mahony to set up a quarterfinal against Argentina.
Although Schmidt is hopeful over O'Mahony, he said his captain looked unlikely to take any further part in the tournament.
"I suspect it probably is," Schmidt told ITV when asked if O'Connell's World Cup was over and with it his Ireland career, having announced before the competition that he would retire from international rugby at the end of the tournament.
"He looks pretty uncomfortable at the moment and I'd say we'll get a scan on his hamstring later tomorrow. We are going to have to wait for some swelling to go down; and that's probably the same thing for Johnny Sexton and Pete O'Mahony."
The inspirational lock with 108 Ireland caps to his name left the field on a stretcher, clutching his right leg, at halftime in the Millennium Stadium.
Sexton, the team's playmaker and hugely reliable goalkicker, was replaced 25 minutes into the game, appearing to leave the pitch in tears after injuring his groin.
He seemed to hurt his ribs making a tackle before receiving treatment on his groin and rejoining the game, only to be put on his back by a crunching hit from Louis Picamoles.
Ireland, who avoided any serious injuries before centre Jared Payne was sent home with a fractured foot on Saturday, lost O'Mahony after 55 minutes of hugely physical rugby when his foot stuck in the grass and he had to be carried off on a stretcher.
"Pete didn't seem too bad, so we're hopeful with Pete. He was walking around okay in the changing rooms so it looks like he's going to be okay," Schmidt said.
"I've spoken briefly to Johnny and he's already talking about next week. I'm not sure if that means he's going to be playing or not but it's probably Paul who worries me most of the three."
Schmidt also said he could ill-afford to lose flanker Sean O'Brien to a ban after he struck France's Pascal Pape in the stomach early in the game.
O'Brien was being held when he swung with an open fist and the coach said he was hopeful that he would not be cited.
