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Actually, Pierre-Emerick Aubameyang have very impressive performance with Barcelona on the first season arriving there, from 17 matches in La Liga he was success scored 11 goals and almost raised 1 goal on every match, but second season after arriving Robert Lewandowski he loss placed as regular position and difficult scoring before return back to Chelsea. But its not really bad after few players departure from Pierre-Emerick Aubameyang until Depay because Barcelona success winning La Liga tittle last season after missing last three season and Robert Lewandowski success as top scorer and stopping Karim Benzema dominance as La Liga top scorer.
Barcelona not required with new striker because they have Robert Lewandowski, Dembele, Ferran Torres and Ansu Fati, seems enough with them for Barcelona attacking line but problem with defender regarding last pre season match conceded 5 goals from Arsenal.
The big gamble that Barcelona made has brought huge profits to the club's finances, Aubameyang was brought in for free from Arsenal, then they sold him to Chelsea for 12 million euros. In fact, Aubameyang is still needed by Barcelona even though they have succeeded in bringing in Lewandowski, but Barcelona don't want to miss this golden opportunity to make a profit after Chelsea are interested in recruiting him.
It seems that Xavi is very satisfied with the striker he currently has, Lewandowski presence has revived Barcelona front line, Xavi still has a stock of quality strikers that he can rely on this season. Barcelona has no problems at all in the defender position, while the midfielder position is already filled with quality players. Gundogan arrival can be a new wall for Barcelona in keeping the central area solid.
If Aubameyang was in Barcelona's attack, Barcelona's attack would have been stronger. Fati and Raphinha are not experienced enough yet. If Aubameyang and Lewandowski were in Barcelona's attack, Barcelona would have been able to maintain the consistency of their performance against the big teams.
Lewandowski is playing well with Barcelona. He was the top scorer in La Liga last season. And yet Lewa's fitness is quite good. Xavi added Gundogan to the squad this season to bolster his midfield. Gundogan is a very experienced player. It is hoped that having Gundogan in the squad will strengthen Barcelona's midfield. Now Xavi should try to tighten up his defense. If the defense is not strong enough, it is impossible to perform well in a competitive platform like the Champions League.