The Colombian forward was left on the bench for the opening day defeat against Manchester City but made an impact when he was introduced.
Arias has a strong record of goals and assists during his time playing in Brazil and countryman Mosquera believes the attacker will have an impressive season and help ease the goalscoring burden on the team.
"I believe in him," Mosquera said.
"He will do this in the Premier League. I think he can score more.
"I believe in him and say to everyone, he's a great player for us.
"He's really important in the national team as well. I think he will be doing really good this season.
"He feels happy, he feels good.