it shouldn't, it's more likely to cause a problem if he applies for another Non-immigrant visa inside Thailand or an extension of stay from one issued outside Thailand. Why not just cancel it?
Thailand isn't keen on damaged passports so as well you got a new one. At a guess I'd say it's going to depend on just how damaged the old one is. I'd suggest explaining the situation to the consulate that issued the visa and see what they say
The visa was used the moment he entered Thailand, what's important are the stamps in his passport. If he has a re-entry permit his stamp will remain live, if he doesn't the stamp will end when he exits
The ask:thailand community, consisting of multiple Q/A groups with over 100,000 members, powers this platform. It is not an official government resource. Our members actively contribute to this resource, and while we strive for accuracy, we cannot guarantee its complete reliability. Assistance to travelers is provided as a community service.