I agree, with good antibiotics, you can get up and running and back to 100% within 3 days.
Something bad or sinister is at play here.
Antibiotics dont work on viruses. They only prevent viral infection you already have to be complicated by another, bacterial disease .
Basically with virus you cant do anything to make you recover better or faster.You just can sit in your room (or in case of stomach bug - in bathroom), drink a lot, swallow pills which reduce fever and not to communicate much with outside world because this sucker virus is highly contagious.Using same bathroom or same dining room probably will infect all other family members.
It can last pretty badly a week or be over quite easily in 2 days, you never know. It is very individual.
That said, I also think there is more than virus in this story. Maybe mental problems, maybe knee, maybe even something more mysterious...Who knows, maybe he already played his last match as pro.( I doubt though he wants it to be Rosol-match, even if he will retire, he proably will play farewell match or tourney on clay )
In any case, he is not ready to play right now and Ferrer takes his place in seeding.