Lewandowski has scored 47 goals in 41 appearances in all competitions for Bayern this season and won The Best FIFA Men's Player award in January.
Bayern were surprisingly eliminated from the Champions League at the quarter-final stage on Tuesday, despite Lewandowski finding the net against Villarreal, who won 2-1 on aggregate.
Oliver Kahn, the Bayern chief executive, said ahead of that second leg the club "definitely" would not sell Lewandowski, who has a year remaining on his contract.
But the former Borussia Dortmund man has been linked with a move to Camp Nou at the end of the season.
Speaking at a news conference ahead of Barca's Europa League quarter-final second leg against Eintracht Frankfurt, Xavi said: "It is not the moment to talk about Lewandowski.
"I respect him a lot as a player, but we focus on tomorrow's match and not potential signings. I will not say anything else about it."
The Blaugrana drew 1-1 in Germany in last week's first leg, where Xavi was unhappy with the length of the grass at the Waldstadion, but he is confident at Camp Nou his players will be able to utilise their possession-based football.
"It's true the pitch wasn't 100 per cent. It is important tomorrow the pitch is good. It should help us improve retention of the ball," Xavi said.
Barca have not lost in 15 games in all competitions, winning 11 of those, and the arrival of Xavi in November has seen the team restore some pride after a dreadful start to the campaign that included elimination from the Champions League group stages for the first time in over two decades.
Despite this form, Xavi declared his coaching job as the "most difficult" in the world, believing the pressure to win as well as play good football makes the Barca role the toughest in football.
"We have an obligation to win and play well," he said. "Imagine what it's like to be at Barca. All week there has been debate about the weekend when we won in the 90th minute [against Levante]. That's what it's like being in Barca. We need to be excellent in everything we do.
"That's why it's the most difficult club in the world. There is nothing to compare it to. In no other country is there a more difficult job.
"We have to win while playing well and that's difficult. Very difficult. It's the most complicated club in the world, I am sure of it."