The Gunners have lost five of their last eight games - with non-League Sutton United and Lincoln City opponents for two of their three wins - to see another Premier League tilt fade as well as their Champions League campaign ended in a 10-2 annihilation at the hands of Bayern Munich.
Sanchez is thought to be restless with the Gunners lack of success and reportedly fell out with team-mates before he was dropped for a 3-1 defeat at Liverpool.
The former Barcelona man was pictured smirking on the bench towards the end of the Gunners' 5-1 home defeat to Bayern, but Sampaoli - facing British media before his Sevilla side take on Leicester City - believes Sanchez has the force of character to make a difference for Arsenal.
"He is a top player, one of the best forwards in the world I would say," Sampaoli said.
"I was lucky to enjoy sharing a time with him in the national team, we went to the World Cup and won a Copa America together. It was a very satisfying moment of my career and great to share it with Alexis.
"He is one of the best strikers in the world and irrespective of the team not going through the best patch of form at the moment, he is a player who can change that.
"Hopefully they will be able to depend on him so he will be able to turn things around as a player within that team."