Kelly made four consecutive Premier League starts before he was omitted from the squad for Saturday's 1-0 loss to Manchester City.
Speaking after the defeat to the Premier League champions, Iraola revealed that Kelly pulled out of Friday's training session with a hip issue.
"I think he has something in the hip flexor," Iraola told the Daily Echo. "Probably a strain. We have to assess him and see how serious it is and when he will be able to help us again."
At the time, Iraola was unsure whether Kelly would recover for Tuesday's contest, but the Bournemouth head coach has confirmed Kelly will miss a second straight game as he provided an injury update ahead of the fifth-round fixture.
"We will see how the players feel today as we are training this evening," Iraola told reporters at Monday's press conference.
"It's not even two days from a very demanding game against Manchester City, understandably some of the players will be very tired. So after training, the decisions on the team will start from there as we need to make the right choices.
"In terms of bigger injuries, the players will be the same apart from Philip Billing, who we have available after the red card. Kelly is missing and will continue to be missing this game and maybe more, we will see."
Iraola will be hoping Kelly can make a quick recovery, having already seen the versatile defender miss all of December with a muscle injury.
Kelly, who has been utilised in the centre and left side of defence, has made 16 competitive appearances this season, scoring his only goal of the campaign in last month's 5-0 FA Cup win over Swansea City.
While Bournemouth welcome back Billing from a three-match suspension, they are still unable to call upon the injured quartet of Max Aarons, Ryan Fredericks, Tyler Adams and James Hill.
The Cherries are still searching for their first victory of the month, having drawn three and lost two of their last five matches.
If Bournemouth can return to winning ways against the Championship leaders, they will advance to the FA Cup quarter-finals for the first time since the 2020-21 campaign.