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Amorim has a good track record with Sporting and as I said before, Manchester United have always had good luck when doing business with Sporting. And the fact that Amorim managed to beat City 4-1 shows that he can compete in the EPL. I don't know if United have the same quality as Sporting at the moment. But this is a good indication that United seem to be on the right track to getting back to success. On the other hand I agree with you. We can't claim Amorim has been successful because he hasn't played a single game with United. The game against Ipswich Town also can't be a reference because Ipswich Town are a lower level than United. I think if Amorim can be consistent with his performance in several games even if it's not a big match, then it can be said that Amorim has succeeded in making United better.
Amorim was quite successful with Sporting. We have seen that Sporting is performing well this season with Amorim's help. Amorim has been able to build a great squad. We can see Sporting's dominance in the last two seasons. Sporting won the Liga Portugal title last season. Sporting was 10 points ahead of second-placed Benfica in the table. Sporting is performing very well this season as well. Sporting has won all 11 matches in the Liga Portugal.
I don't think Manchester United's squad is weak at all. Their main problem was the coach's strange match strategy. Hopefully Amorim will take the necessary measures to stabilize Manchester United's performance. However, I don't think Manchester United's performance will improve dramatically this season.