The Colombian midfielder was substituted after less than half an hour during the Saints friendly at Weymouth after he gave away a penalty and Poortvliet has now subsequently banned Viafara from training until he gets his attitude right.
"I told Jhon he could not train with us until he is good in the head. His family are in Colombia and he is homesick," Poortvliet explained.
"He has to resolve the problem. When he is settled in his head then he is welcome but until then he is not welcome because when you are here you have to be 100 per cent involved for Southampton.
"I don't know what will happen. He has to go to the chairman or his agent and resolve the problem and then we will move on."