Now is not the best time for Portuguese football. A few years ago, teams from this country, played in Europe very strong. I do not even know what the decline in the level of the Portuguese teams is connected with?
Why do you say that? Let's just look at the Champions League, we have the Top3 Portuguese teams there. I can agree with you if we talk about Benfica, because not only they have lost all three matches they played, but they also got a very heavy defeat vs Basel. The thing is they are not doing very well this season on Portuguese League, so I would say that is a problem with Benfica and not with Portuguese teams in general.
If you look at Sporting and Porto, they are doing ok. Sporting is no match for Barcelona and Juventus, the only thing they can do is win vs Olympiakos, which they did, and try to play well vs Juve or Barça, which I think they did as well.
As for Porto, they are in a very competitive group as well, with a lot of rich teams. Monaco won the french league last year (that has PSG in it, so it was a big deal), and Porto manage to defeat them. Leipezig finished in second on bundesliga, and is in 3rd place right now just one point bellow Dortmund, so they are not an easy team and Porto played well vs them, and could have done better because the first goal they suffered resulted from a mistake form their GK.
Right now I think they are doing quite well, and Porto can still advance to the next phase, and Sporting can still do something in Europa League, so I don't think they have declined that much, from what they normally do.