Al Nassr losing, specially in a week like this, was TERRIBLE for them, couldn't be any worse timing. Not only they are keeping the distance with Al Hilal the same when they could have cut it by three more points, but they also lost their position to Qasadiyah and now fourth as well, behind three points and have to chase them. They could have been just one points distance to second place, now they are fourth place, and that's terrible.
And not like they played some amazing team neither, Al Ettifaq is 9th and to be fair Al Nassr should have won this game with ease, without any much trouble, and the fact that they are losing this makes it even more troublesome. I do see them as good, so maybe Al Nassr could reach third place, but thats about it, I do not see second place as option anymore.
Basically, there is no guarantee for Al Nassr to be able to finish in third place, because they are not as good as Al Hilal and also not as good as Al Ittihad, because the reality is just to compete with Al Qadisiya, it is already overwhelming for Al Nassr to get and stay in third place. Thus, I think it will be a natural result if for example later Al Nassr really fails to finish in third place but for now, at least Al Nassr still has a chance to return to third place.
About Al Nassr's defeat at home by Al Ettifaq, if we analyze Al Ettifaq's results so far this season. In fact, Al Ettifaq has good results only when playing away from home, so it is not surprising that Al Ettifaq also managed to beat Al Nassr with a score of 2-3. At least, the scoreline also proves that their match was a tough one as all five goals came in the second half.