The Ivory Coast international, who turns 30 on November 10, has yet to agree a new deal with the Eagles, which mean clubs from outside England could approach him in January.
Vieira, though, insists it remains very much business as usual as the south London club look to maintain their Premier League progress.
"It is not (a distraction) for him and it is not for the football club as well," the Palace boss said.
"We know how important it is for us and, again, he knows how much the fans, the club love him and we know how much he loves the football club as well.
"So the decision has to be his decision, and we will do everything in our side to keep him because he is an important player for the football club, but then we will see.
"At the moment, he is playing well, is performing well, and that is all that matters for now."
Vieira told a press conference: "If you take any player in the Premier League and you mention those names (of leading European clubs) to those players, that of course will have an impact.
"And when big teams like that have been mentioned, of course for any players in the Premier League, that creates an excitement.
"It will be his decision. Me as a manager and we (as a club) will do everything that we can to convince him to stay with us and to make him understand.
"The next couple of years can be really exciting for the football club, and of course we want him to be part of it. It is about where we want to go next.”
Additional reporting from PA