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There is still a possibility that they in a good performance, considering they have an experienced coach, but without a key player like Vini Real Madrid performance may not be really good.
Before against Atletico Madrid in matchday 6, I mean next match on matchday 5 Real Madrid will also against Real Sociedad, without Vini Jr. I think Real Madrid will difficulties to got three points. But let's see in that match first, whether the Real Madrid team is still in good performance or not. If not, then things will be difficult for them against Atletico Madrid.
Last season Real Madrid had difficulty winning their home match against Real Sociedad. Real Madrid drew in the home match, while Real Madrid had to admit defeat when they visited Sociedad headquarters. Of course Real Madrid will try to improve at their meetings this season even if they are not strengthened by some of their pillars including Vinicius.
I believe Real Madrid is fundamentally not a worthy opponent for Real Sociedad considering the two's match record. In the last 36 meetings, Real Madrid was able to pack 23 wins, 6 draws and only 7 defeats. This means that it is highly probable that Real Madrid are the favorites at home despite their poor results last season against the same team.