Joe Schmidt hopes Henshaw can return for Romania as Fitzgerald gets midfield nod
The Ireland coach has opted to select Luke Fitzgerald at inside centre alongside Jared Payne after losing the Athlone native.
However, the New Zealander remains confident that his first-choice No12 will play a part in the pool stages, with the injury at the lower end of the scale.
"Robbie, right at the end of training on Tuesday, felt his hamstring tighten a little," Schmidt explained.
"We got it scanned, there's a bit of blood there. OK to walk and jog, but he does feel tightness and it would be a risk to push him. He should be OK for next Sunday."
It means Fitzgerald makes his World Cup debut in a relatively unfamiliar position.
"This time four years ago Luke was starting at No12 for Leinster, he's had a fair bit of game time for me at 12 and we have confidence in him. He has played at No13 in the pre-World Cup matches and deserves his opportunity," Schmidt said.
Paul O'Connell will captain the side against the Canadians who are without their key player Tyler Ardron who is ruled out with injury.
The Ireland skipper will be partnered in the second-row by Iain Henderson whose form against France has been rewarded with a starting berth at the Millennium Stadium.
Dave Kearney is another whose form has been rewarded with a start on the right wing alongside his brother Rob.
"Going back two years, Dave Kearney was exceptional," he said. "Andrew Trimble too, but unfortunately he was right in the frame and picked up a second injury and the timeframes were tight. Dave was playing well and deserves an opportunity.
"Iain has played very, very well but Devin Toner has done a super job for us over last two years and there is going to be a real contest."
Although Ireland are heavy favourites to beat the Canadians, Schmidt has plenty of respect for them.
"Canada have guys who can turn a game around very quickly and have a number of guys who play Sevens and are used to a turnover attack. I know Jamie Cudmore well from my Clermont days and the power he brings," he said.