Had this happen to my previous Cham. This is likely one of two things:
1) An Injury - caused by him shooting and hitting something, or a feeder going in his mouth in a weird angle and possibly scraping/scratching his tongue...
2) More than likely , he has a calcium deficiency. Calcium is needed for muscular functions i.e his tongue. If you feel he's getting enough then it may be a lack of UV light which would allow him to absorb it. You need to up his calcium intake and exposure him to a few hours of natural sunlight daily, asap. They deteriorate very rapidly, when they can't shoot their tongue in my experience. Not sure where you live but if you can't get him outside, then up his calcium with D3 supplementation for a short time. Exposing him to natural sunlight is safer because his body will only generate the amount of D3 it needs, vs with supplementation you run the risk overdosing.