Yes. Doctors in Hong Kong first observed that patients who had moderate to severe cases but had recovered would be absolutely winded walking down the hallway are up a flight of stairs. They gave chest x-rays and said that the scar tissue in the Lungs resembled Stained glass. Subsequent Testing of patients lung capacity revealed a significant decrease. Whether it’s permanent or whether it can be brought back to normal/ near normal with conditioning and therapy is currently unknown.I haven’t seen much about the lung since since this all started. Like in March there were a lot of stories about the lung damage. Now, not so much. Has this been confirmed or they just thought this at first?
also just require mask usage during training
Here’s a link from Johns Hopkins. The TL;DR is that The worse your case, the more likely you have serious damage.

COVID-19 Lung Damage
COVID-19 can cause lung damage and breathing problems that can persist even after recovery. An expert in lung disease explains.