The two teams meet later tonight.
Bielsa said earlier on Monday: "The calendar is so overcharged it doesn't bear in mind the development of the preparation.
"That's why I have serious doubts over the future of professional football because it is constantly commercialised and the product every time is constantly worse."
Asked about Bielsa's comments, Viera responded: "I think the way that Leeds play is really demanding and obviously a lot of energy game after game is really difficult to maintain.
"But I think when you look at the game as well, they've been really unlucky in some of the games where they should have scored and they didn't.
"I think at the moment things are not going their way but that doesn't take away the energy and the quality that they have.
"Regarding the physicality from last year to this year, it is difficult because I didn't watch them play so many times last year, but this is the team that for me, play with organisation and energy, and that didn't change, really.
"So I think they've been unlucky not to win a couple of the games that they played so far.
"And reading the calendar, I think it's the same for everybody. So we just have to adapt to the number of games that we have to play."
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