William Saliba talks about signing his new long-term deal at Arsenal ahead of their Champions League game vs. Olympiacos. (0:37)Open Extended ReactionsMikel Arteta has backed Viktor Gyökeres to thrive at Arsenal by insisting the "ceiling" to what he can achieve is "very, very far" from his current performance level. Viktor Gyökeres has scored three goals in six Premier League games. The demands that he puts on himself every single day, it is a joy to work with him," Arteta added. The ceiling is very, very far to what he can give still give to the team so very happy with him."