The 22-year-old Iceland international limped off during the first half of the Bluebirds’ 3-1 victory over Bristol City on Saturday.
He will miss Brighton's visit to Cardiff City Stadium on Wednesday and the team’s away trip to Burnley on Saturday.
“He should be about a week or so," Cardiff boss Malky Mackay commented. “It's not as bad as we thought it would be considering the way he limped off.”
Cardiff currently sit at the top of the Championship.