Omaha, Neb. – Nebraska receiver Tyjon Lindsey and walk-on defensive lineman Dylan Owen were hospitalized recently after falling ill during winter conditioning drills.

Coach Scott Frost confirmed to The Lincoln Journal Star and Omaha World-Herald on Tuesday that both players have returned to the team. It was unclear when the players became ill, though Lindsey tweeted a request for prayers for his health on Jan. 23.

Lindsey was in the hospital for three days and Owen for two. Frost told the Journal Star both were treated for rhabdomyolysis, a potentially life-threatening condition that occurs when muscle tissue breaks down and leaks into the blood. The condition can cause kidney damage.

Frost and head football strength and conditioning coach Zach Duval were not made available for comment to the Associated Press.

Athletic director Bill Moos, in a statement to the AP, said, “First, I fully understand the seriousness of this situation. I have total faith and trust in Scott Frost as well as his staff. One of the things that impressed me most during our discussions surrounding Scott’s hiring was his total commitment to the safety and well-being of his players.”

Frost, who was hired away from UCF in December, told the Lincoln newspaper the players’ illness was caused by a 32-minute weight workout he characterized as “fairly intense.”

“We had trainers in the weight room during the workout to pull guys out of the workout if they saw any problems,” Frost told the Journal Star. “Despite all that, we still had two kids that ended up having problems. Our players are our No. 1 concern. We thought we were approaching everything safely and the right way and it turns out that it was a little too much for a couple of them.”

In 2017, Oregon suspended its strength and conditioning coach after three football players were hospitalized following overexertion that led to muscle cramping and other symptoms. In 2011, 13 Iowa football players were hospitalized for rhabdo after an offseason workout, and in 2016 the university paid $15,000 to settle a $200,000 lawsuit brought by one of the players.

Jay Hoffman, director of sports and exercise science at the University of Central Florida, said it was alarming how often rhabdo occurs during offseason conditioning.

“It shouldn’t be considered the cost of doing business,” said Hoffman, a former president of the National Strength and Conditioning Association. He said he did not know Frost or Duval from their time at UCF.

Frost told the Journal Star that the hospital stays for Lindsey and Owens were mostly precautionary.

“Anything that happens in our program is ultimately my responsibility,” Frost said. He added: “I want to make sure people understand that the health of our players is always going to be our primary concern. It’s been kind of a scary deal and both kids are doing fine now.”