If he throws a Side-Kick, try this...
Assuming its with his RIGHT leg deflect it away with you RIGHT forearm. Almost simultaneously you should "dip" in low and hit his fixed LEFT leg with a RIGHT low-kick. Might trip him or knock him off-balance.
One thing Ive learned about fighting against Kyokushin and Taekwondo fighters they tend to lack proper boxing skills. Not trying to generalise but i notice a lot of bad karate habits creeping into their thaiboxing strategy... also most karate styles dont punch to the face - so when they are in a situation where they are called to "box" their punches may seem a bit awkward. Even great fighters like Andy Hug and Francisco Filho struggled somewhat with boxing when they first starting fighting in K-1.
But - assuming his boxing skills are decent enough to negate the above paragraph... with his Taekwondo background expect him to use his kicks. Expect back-kicks, spinning-back-kicks , all sorts of high kicks. And lot of kicks to the mid-section.
When i spar against a "kicker" I try my best to keep it close range so that Im out of range of any high kicks he might want to throw. I'll only open the distance if im planning to throw a high kick (even then you should not allow him a moment to throw one). Keep close with knees and tight punches... push him away for leg strikes.
IF he comes in with kicks try and trap them - grab his leg - get you other hand around his neck and twist him off balance - then close the distance and kick/knee to his head.
If he's throwing high kicks - as soon as you block one move in with a flurry of punches before he's got his footing. With luck his guard should be down and he should be off balance...
Work around that... listen to you corner... DONT PANIC... stick to the combos you've drilled into your head... use your strengths... agression is important - use it if you can.
good luck.
