Speculation emerged at the weekend linking the Red Devils with a move for the Uruguay international striker.
Cavani only switched to the French champions last summer in a £55million move and has gone on to score 17 goals in 24 appearances.
While Blanc says he cannot stop other clubs coveting his players, admitting the French side themselves are interested in new recruits, he believes it would be near-impossible to take one of their top stars this month.
Speaking at a press conference on Friday, he said: "You cannot prevent that some club is interested in PSG players, as we are interested in many players.
"But today, it is almost impossible to take a major PSG player during the winter market."