It isn't nesscessarily bad for him. He might be bored so try more toys. Do you have more than one piggie? It would be great for him to have another cagemate. Guinea pigs need to have a piece of wood in there cage all the time to gnaw on. It will grind their teeth down. I have a house made of wood that keeps my pigs occupied and away from the chloroplast.
I only have one piggie and asking my parents about getting another one. What are so toys i could put in, he didn't like the tennis ball, I have a ramp to go up to the second level and that is made of wood and he chews on that some times.