Right, but his problem is the same that a marathoner has. The body has about 2k calories or so of glycogen available for use--when it runs out of that, then it "hits the wall" (as the term is in marathoning--this typically happens to untrained people at the 20 mile mark or so--trained people who hit it usually started out too fast and "blow up"). It usually happens at different points for different people depending on how efficiently their bodies utilize their glycogen stores and, sometimes, if their bodies have increased their glycogen stores or utilize fat stores for energy. Once they hit the wall, things get ugly.
Depending on how intensely this guy is playing and how long his matches are taking, he could be running his glycogen stores lower than needed for his body to feel itself to be capable of exerting maximum effort. That's why I recommended the energy gel while in the meantime he might try to improve his conditioning.
People tend to think of marathon-type endurance athletes like they're either aliens or like they're doing something equivalent to light jogging for 26 miles. To run a reasonably respectable one, you're running at sub-7 minutes per mile the whole time. That takes muscle glycogen.