However, Zola had better news for Blues midfielder N'Golo Kante.
"It's not an easy one," said Zola.
"I think it's a serious injury, on his (Callum's) Achilles tendon. I cannot tell you the full extent of his injury. I think he will have to have an examination but it's not looking good.
"N'Golo was taken down and he fell on the foot of a player, so he had a contusion in his ribs. He couldn't breathe properly, but he will be alright."