The 25-year-old Chelsea man has been tipped by many as a replacement for the injured Neymar, though Bernard is said to also be in the frame to deputise.
Willian has suffered an injury scare of his own in training but could still be picked for the last-four clash by Luiz Felipe Scolari.
“A lot – especially on defending,” the Brazilian said. “He always demands a lot from us. I have had a good experience at Chelsea.
"I have played a lot of games and run a lot for him. I hope I will learn a lot more over my next four years at the club.”
That defensive work-rate has been noticeable over the past few months - and not just from Willian.
As Opta stats show, another Chelsea midfielder has won 20 tackles so far this World Cup - the highest of any player.
That midfield man, Oscar, has no doubt been on the receiving end of the same pointers as Willian from his Portuguese coach. The pair's seeming willingness to track back will serve them well in terms of keeping them in Mourinho's good books.
As for the 25-year-old himself, who was brought to Stamford Bridge for £30 million last season, every blade of grass he covers will likely prove crucial against Germany.
The absence of Neymar will surely be felt by the Brazilians, while captain Thiago Silva will also miss out in defence if Brazil's appeal against his suspension is unsuccessful.
A nation will be relying on Willian if he starts, then, while Mourinho should be watching eagerly too.