Does his velocity SEEM to have dropped or has the dropped been measured? No arm issues at all–other than the loss of velocity? Did he have a growth spurt? Has he changed anything significant in his mechanics recently?
If it’s measured, he’s probably fatigued and needs to miss at least a start and have his throwing limited during that time.
If the velocity doesn’t come back after that, then it’s perhaps time give him for 2-3 weeks away from pitching then see what you’ve got.