According to Sport1, there was already "a certain degree of discontent in the highest circles of leadership" after Bayern Munich's 0-0 draw at Schalke on September 5, though that frustration was not directed solely at the Colombian. Díaz had chances to win the game but, like several of his teammates, could not find a way past Schalke goalkeeper Loris Karius.
The 29-year-old has continued to squander presentable opportunities since, scoring just once so far this season despite featuring prominently in Bayern's attack. In the narrow 2-1 win over promoted SV Elversberg last Sunday, Vincent Kompany left Díaz out of his starting XI for the first time this season, hoping his pace and energy would provide an impact from the bench.
The plan backfired when Díaz wasted another clear chance shortly after coming on, at one stage sending teammate Josip Stanišić into visible frustration on the touchline after Michael Olise picked him out inside the box, only for Díaz to fluff a first-time finish by trying an unnecessary backheel.
Sport1 reports there is now genuine "bewilderment" inside the club at his performances, with speculation growing that Díaz could be given an extended break, particularly given the demanding run of international travel he faces with Colombia.
The winger is set to play matches in the United States during the upcoming break, before a further trip to Australia in November, continuing what has already been close to two years of almost uninterrupted football stretching back through last year's World Cup.
Kompany, for his part, has publicly backed his forward, insisting the issue is one of composure in front of goal rather than any deeper problem with his game.
"It's all about finishing," the Bayern head coach said after the win in Saarland. "His energy consistently creates danger."
Bayern have previously found that a short spell out of the side can reset Díaz's form, with a brief suspension-enforced break in December last year followed by a strong run after the winter break, and the club may look to repeat that approach given his current struggles in front of goal.