Bayern Munich claim Robert Lewandowski does not want to leave the Bundesliga champions, adding clubs "risk a FIFA penalty" if they negotiate with the player.
Sky Sports News HQ reported earlier on Wednesday that United and Chelsea want to sign the Poland striker this summer and had both held initial talks with his representatives.
The Bundesliga champions told Sky Germany: "Lewandowski does not want to leave Bayern. There are no talks with other clubs and there won't be any.
"Lewandowski's contract expires in 2021. He signed it not long ago. If other clubs negotiate with long-term contracted players they risk a FIFA penalty."
Lewandowski scored 30 goals last season but missed out on the top-scorer prize to Borussia Dortmund's Pierre-Emerick Aubameyang, who scored his 31st on the final day of the campaign.
The 28-year-old said recently that he was "disappointed" over a perceived lack of support from Bayern in his hunt for the Bundesliga's golden boot award.
He told the Polish Super-Express newspaper earlier this month: "I was not really happy with how my team helped me. I was annoyed and disappointed with the team's attitude."
And his agent Maik Barthel told German football magazine Kicker: "He was disappointed as I have ever seen him before.
"Robert told me that he got no support and that the coach (Carlo Ancelotti) gave no call to help him win the top-scorer title in the last game."