RIVERHEAD, N.Y. (CBSNewYork) — A Long Island high school football player was in critical condition after getting sick on the field during practice.

Doctors said the 16-year-old now faces weeks in the hospital because of heat stroke.

Nikolas Visco collapsed Monday, on Riverhead High School’s football field. The junior was practicing outdoors for 3 hours in oppressive humidity with temperatures in the 80s.

He was rushed to the hospital with a temperature of 108 degrees.

“He was on a mechanical ventilator by the time he got to us, disoriented with altered mental status,” Dr. Daniel Sloniewsky told CBS2’s Carolyn Gusoff.

Visco’s condition quickly worsened. His kidneys and liver shut down, as he displayed signs of heat stroke.

Visco’s family thanked his teammates for support and asked for privacy as he remains gravely ill.

Parents near the school said they worried about their kids in the heat.

“It’s scary. You think it’s not that bad, but it is,” one parent said.

Doctors said heat stroke can happen faster than most people realize.

As Stony Brook’s team doctor explained, the key for athletes in the heat is hydrating continually.

“Make sure they are drinking around the clock to get ahead of this problem. If they get onto a field and they are dehydrated, it’s too late,” Dr. James Paci said.

Dr. Paci recommended monitoring your child’s body weight before and after practice. A loss of a few pounds is a sign of dehydration.

Experts suggested filling up with water, sports drinks, fruit, and salt, and avoiding energy drinks packed with caffeine, which worsens dehydration.

Players need to recognize warning signs like thirst, headache, dizziness, and the absence of sweat.

Riverhead school officials said they practiced under a self-imposed modified heat alert on Monday, working out in t-shirts and shorts with frequent water breaks.

Visco’s prognosis remained unclear on Friday, his doctors said there are encouraging signs of improvement, but damage to his kidneys could be permanent.

Schools on Long Island must suspend play if the heat index reaches 95 degrees, on Monday the heat index was 92.