[TFT] Morde's health bar turned red and won't let me sell [GAMEPLAY]

Was playing TFT and had 2 Mordes on my bench. I went to sell the Mordes and one of them turned into an enemy Morde. His health bar became red and I wasn't able to sell him. I put him on the field and he still wasn't able to sell. He was stuck on my bench the rest of the game and took up 1 of my 9 slots.