The 18-year-old joined Porto from Jagiellonia Białystok during the January transfer window and has already made an impression in Portugal. He has contributed four goals and four assists in 22 competitive appearances since his arrival.
Pietuszewski attracted significant attention during the summer, when Manchester United, Arsenal, Chelsea, Liverpool and Manchester City were all linked with the Polish international. He ultimately remained at Porto, but interest from Europe's leading clubs has continued.
According to Sky Sport Germany, Bayern have now made the winger a concrete option as they consider their attacking requirements. The German champions are looking for an alternative to Díaz on the left flank, and Pietuszewski is among the players being assessed.
Bayern sporting director Max Eberl is reportedly a strong admirer of the teenager, while discussions have already taken place regarding a possible move.
Pietuszewski has a reported release clause of €60 million in his Porto contract, which could make any deal a significant investment for Bayern. The clause gives the Portuguese club a degree of protection as interest in their young attacker grows.
Bayern are not focusing exclusively on the Porto player, however. The report indicates that several other candidates remain on the club's wish list as they assess possible additions to their forward line.
The search for another option behind Díaz reflects Bayern's desire to strengthen their depth in wide attacking positions. Pietuszewski's ability to operate as an attacking winger, coupled with his early contribution in Portugal, has put him firmly in the picture.
Having resisted interest from several Premier League clubs in the summer, Porto could now face another challenge to keep the teenager. Bayern's interest is described as concrete, although no agreement has been reported and the €60 million clause represents a substantial obstacle.
For Pietuszewski, the attention is another indication of how quickly his profile has grown since moving to Portugal. Bayern will now have to decide whether to pursue him ahead of their other attacking targets.