Gravenberch was left out of the travelling squad for the match in Turkey after failing to shake off the discomfort that also restricted him ahead of Sunday's 1-0 defeat by Arsenal, when he remained an unused substitute.
"It's a day-to-day thing. It's a fracture of the heel, and it's about the pain... The other day against Arsenal he was warming up but was not fully confident, and he hasn't improved since then," Iraola told reporters on Tuesday.
"Every day we ask him, every day we see how he is. If he can be available for the weekend, lovely, he would be a very good help for us. But I cannot tell you right now," he added when asked about the 24-year-old's chances of returning for Sunday's trip to Crystal Palace.
The Spaniard also backed teenager Trey Nyoni after the 19-year-old was handed his first Premier League start against Arsenal.
"He has to continue in the same place he's been since the start of pre-season, being ready for every game," Iraola said. "He's been involved in most of the games lately, so we trust him."
