The Saints top scorer landed heavily on his right knee midway through the first half at the Etihad Stadium and had to be stretchered from the pitch in agony while his teammates looked on in horror.
Though the swelling is so bad that no instant diagnosis can take place, the talk behind the scenes was of ligament damage that will end Rodriguez’s season and his chances of going to Brazil with England.
Manager Mauricio Pochettino refused to speculate on the extent of the injury but his tone clearly suggested it was likely to be very serious.
“To be completely honest it’s not looking good,” said the rueful Saints boss.
“We need to assess him today and tomorrow but it’s not looking good.
“It’s not going to be good for him, it’s not good for the team.”
He added: “I can’t really know exactly what’s wrong with him or when I’m going to see him again in a Southampton shirt.
“We need to analyse him today and tomorrow and know the exact reality of his injury.
“All the players are really affected, not just about the result, not just about the refereeing decisions, but more than anything about the doubt of how severe his injury is.”