All fans hope that Mbappe can perform as well at PSG with Real Madrid. But right now, I think Mbappe is in the process of transitioning to a different playing pattern with a different coach and teammates. Mbappe is a good center forward and has speed, but Real Madrid does not have a game scheme that relies entirely on center forwards. Mbappe's finishing in some matches may not be good, but over time he will get back to his best performance.
Transitional phase of Mbappe in Real Madrid is likely over because I see his performances are improving with time. The injury came at bad time when Mbappe shown some strong signals of his better adaptation in Madrid, scoring more goals and playing better for them. The injury will take extra time for Mbappe to return and play well again. Real Madrid and their fans will have to calm down, give Mbappe more time and they must know risk of forcing Mbappe to play too early after the injury. Sometimes in bad situation it will make his injury worse and it damages plan of Real Madrid for a long season with many competitions they are participating in.
However, in most cases, many players who experience injuries after the international break are so intense that they will definitely play the full game, but if you look at Kylian Mbappe's condition, it seems that he will be able and ready to be fielded as a starter against Celta Vigo, regarding scoring goals, it all depends on Kylian Mbappe's physical condition, whether it allows him to score goals or not, hopefully Kylian Mbappe will be able to score goals in the match later.
Mbappe has great skills and experience to score goal if you give him a half of chance or a chance, but with his super star position, he will get more attention from opponents that will assign considerable defensive resources to control him. When Mbappe is not ready in fitness, he will have less chances to score goals because as said opponents always try to minimize open space and chance for Mbappe to threaten their goalkeeper.
In not too good fitness, performance of Mbpape will depend more on support from his team mates. It is an alarm for Mbappe on need of building good relationship with his team mates in Real Madrid.