Things are getting testy between UFC's Yair Rodriguez and Zabit Magomedsharipov ...
The two were SUPPOSED to do battle at UFC Fight Night on August 29 -- but that's been pushed after Yair suffered an ankle injury.
Zabit -- the #3 ranked featherweight contender -- ripped Yair about the situation on social media saying, "Yair has no balls."
Zabit then called for a replacement fight with the champ, Alex Volkanovski ... a fight Alex seems to be interested in taking.
The whole situation didn't go over well with Yair -- the #5 ranked featherweight contender -- who clapped back at Zabit Thursday morning.