The 32-year-old is keen on getting game time before the World Cup finals.
Vieira said: “I still have a year left on my contract and I count on seeing it out. But if my coach at Milan was to say to me that he no longer wanted me, I would leave the club.
“Paris St Germain and Lyon can be good challenges. What’s important for me is to play before the World Cup. It will be a sporting decision.”
