Five players on Tufts University’s men’s lacrosse team have been hospitalized after a workout with an alum who is a graduate of a Navy SEAL training program, according to the university.

Patrick Collins, executive director of media relations at Tufts University, said in a statement to NPR on Sunday that 12 players participated in a “voluntary, supervised 45-minute workout” on campus last week and have been diagnosed with rhabdomyolysis. As of Friday, five players remain in the hospital, he also said.

“Both the number of confirmed cases and the number of those hospitalized could change. Our thoughts are with the players and their families, and we are hoping for their quick return to good health under the care of local medical experts,” Collins said. “Meanwhile, we are closely monitoring the condition of the rest of the team and have postponed all team practice activities until each team member has been evaluated and medically cleared to return to participation.”

The condition, also known as rhabdo (rhabdomyolysis), happens when proteins and electrolytes from damaged muscle tissue are released into the bloodstream, according to the Centers for Disease Control and Prevention. This could damage the kidneys and lead to kidney failure, seizures, permanent disability and even death, the agency also says.

The condition can affect anyone, but athletes, firefighters, those who work outdoors and those who work in hot environments are at higher risk for developing rhabdo, the CDC says.

The university is also “appointing an external, independent investigator to conduct a thorough review as quickly as possible, with a goal of taking any steps needed to support the safety of our student athletes,” Collins said.

The alum who led the training most recently graduated from the Basic Underwater Demolition/SEAL training program, or BUD/S, Collins also said. The program is an intense, monthslong training program for Navy SEAL candidates.

NPR has reached out to the U.S. Navy for comment.

In May, the university’s men’s lacrosse team won their fourth NCAA Division III national championship game.