Of course Walker's injury is a heavy blow for Manc City. because for Man City he is a mainstay defender and also Walker is one of the pillars of Man City's defense and last season he played a big role in bringing the team to the treble. Of course his absence will be a big problem for Man City, which has the ambition to defend the EPL and UCL titles.
It can be big issue for Manchester City and can be not. Last season, there were months when Pep Guardiola did not use Kyle Walker and Manchester City still played well. He can do it again this season but get this big change before two important matches with Real Madrid can bring some unplanned things for Pep. With his flexibility as shown through his coach career, Pep can adapt to this problem very well.
Not only was Vinicius smiling broadly when he saw Walker's injury, Arsenal were also smiling broadly because Walker was in danger of being absent when Man City faced Arsenal. We all know that the match against Arsenal is the most crucial match to win the EPL trophy this season because the distance between Man City and Arsenal is only one point.
Vinicius is a player from Real Madrid and he had reasons to smile like that. It shows how he imagines difficulty of defense from Kyle Walker if he has to face with this defender.
Manchester City can have other wing back to replace Walker and can replace him in defense but in attacking support, it will be harder for them. Arsenal will have a big match with Manchester City after International break and this injury of Walker brings some advantage for Arsenal.