The fly-half had to go off in the second half of Ireland’s 29-10 win over Italy in the warm-up match in Dublin.
“The good news is that he has had an X-ray and it is not a fracture. We will give it time for the swelling to go down,” said Schmidt.
Carbery, 23, started instead of the rested first-choice Johnny Sexton.
“It looks like a ligament injury, the ankle looks pretty stable and we would be hopeful it is not too bad,” Schmidt added.
Munster player Carbery scored the first of Ireland’s five tries at the Aviva Stadium, the others coming from Dave Kearney, Andrew Conway, Jordi Murphy and replacement scrum-half Kieran Marmion.
Schmidt impressed by Farrell display
Ireland will continue their preparation for the World Cup by facing England in two weeks’ time at Twickenham before back-to-back games against Wales the following two Saturdays.
Schmidt confirmed Sexton will be available to feature in the next warm-up clash at Twickenham on 24 August.
“Johnny probably could have played this weekend,” said Schmidt.
“He trained in the week and was going pretty hard.”
The Ireland coach acknowledged Munster centre Chris Farrell had boosted his chances of forcing his way into Ireland’s 31-man World Cup squad by producing a fine display.
“He took a step toward it,” said Schmidt of Farrell.
’31-man squads too tight’
Schmidt will have to trim Ireland’s current 43-man squad to 31 before they travel to Japan and the Ireland boss believes World Rugby should have allowed teams to bring additional players to the tournament.
Ireland will launch their World Cup bid by taking on Scotland on 22 September, before facing the hosts six days later – and Russia just five days after that, with their concluding pool game against Samoa.
“With 31 players, I think it’s a very tight number that World Rugby limit you to,” said Schmidt.
“They talk about player welfare, but we have a six-day turnaround into a five-day turnaround, and 31 players, it’s very, very complicated.
“And all the teams, I’m not saying that’s just tough for us. All the teams have tight turnarounds at stages.”
Schmidt’s squad head to a warm-weather camp in Portugal on Wednesday before travelling straight to London for the Twickenham game.