According to the 34-year-old's club Matsumoto Yamaga, the defender collapsed on the pitch after finishing a 15-minute warmup run and is believed to have suffered a cardiopulmonary arrest.
The former Yokohama Marinos player was reportedly rushed to the hospital but was unconscious upon arrival.
Matsumoto president Hiroshi Otsuki has indicated in a news conference that the veteran's condition is "extremely severe".
It remains unclear if his collapse is linked with the record high temperatures across Japan that have caused a rise in heatstroke cases, which saw a total of 43 people died in the past two months.
Matsuda played 40 times for Japan, including at the 2002 World Cup, which was held in Japan and South Korea.