The Frenchman's season is over due to the setback.
Despite that, Setien tried to send a message of positivity as the club wait to see how long the French forward will be out of and if they can make a signing on an emergency basis.
"I am worried about Dembele, not just as a footballer, but as a person because he's an extraordinary kid," the coach said. "He was so motivated and excited in training.
"I am gutted that he can't play football for a number of months. He doesn't deserve that because he's a great person. I care more about that than anything else.
"We're waiting to see how long it will be, then we will have to talk. Once we have the information, we can take decisions, we will see if we are able to sign."