Offensive lineman Doug Brenner, tight end Cam McCormick and offensive lineman Sam Poutasi are patients at PeaceHealth Sacred Heart Medical Center at RiverBend in Springfield, Oregon, the hospital confirmed to ESPN.
"The safety and welfare of all of our student-athletes is paramount in all that we do," Oregon said in a news release.
"While we cannot comment on the health of our individual students, we have implemented modifications as we transition back into full training to prevent further occurrences. We thank our medical staff and trainers for their continued monitoring of the students and we will continue to support our young men as they recover. "
The Oregonian reported that Poutasi's mother said her son had been diagnosed with rhabdomyolysis, a condition in which skeletal muscle tissue is rapidly broken down and products of that process are released into the bloodstream.
Depending on the severity, this can be harmful to the kidneys and may lead to kidney failure, according to the U.S. National Library of Medicine.
Multiple sources described the workouts to the Oregonian as "akin to military basic training, with one said to include up to an hour of continuous push-ups and up-downs."
However, a source told ESPN.com that the workouts weren't as strenuous as The Oregonian reported, using the example that players haven't even started using weights yet.
Oregon players chimed in on Twitter late Monday evening after reports surfaced.
The workout was not even what the media is portraying it to be 🙄— U.Amadi (@UAmadi14_) January 17, 2017
The workouts are just fine. Don't be so quick to assume the media is correct and believe the players, Coach O is getting us right.— Brady Aiello (@BAiello66) January 17, 2017
The Oregonian's report went on to say that some players complained about discolored urine, and others were found to have "highly elevated levels of creatine kinase," an indicator of rhabdomyolysis.