While still running second, efforts were made to boost the 33-year-old's electrolytes at the final pitstop, but that made little difference.
"He always just wants water," Ryan said. "He doesn't drink much in the race.
"I think back to the preparation he had too many days of not having set times for his lunch and dinner and all of that sort of stuff that he really works hard on.
"That's probably affected him and he was really tired. We've got to think about it next year, hindsight's easy.
"We should've said no to all the media people and made sure we had our driver prepared, but it's part of the sport."
Reynolds indicated he would seek medical advice, and Ryan said the team had been approached by "people who want to help with the human science sort of stuff" before it had even left Bathurst.
"It was people who want to do some tests with him as quickly as they can so they can work out where his levels are and whether it's a diet thing or whether it's just a coincidence because of all the lead-up," he added.
"We'll support whatever he needs to do. It might not need much, it might just mean he needs to change his diet if he knows he's going to have a big stint like that."