Gomez, 29, was forced off inside the opening 10 minutes of Liverpool's victory in Nashville last week.
"Joe has a muscle injury. I think it was quite clear since he complained straight away, so it will depend how he evolves, but he will be some weeks off," Iraola told reporters.
"It's not massive, it's a normal muscle injury, but I think it's going to be impossible to have him for the start of the season because we are not so far away."
Gomez's injury leaves Liverpool facing a defensive setback as they complete their preparations for the new season.
Liverpool, who finished fifth last term, begin their Premier League campaign at Newcastle United on August 23.