The Brazilian centre half has impressed since coming into the back four against Southampton earlier this month.
Monreal believes there is a lot more to come from the 25-year-old, who signed from Villarreal just over a year ago.
When my English got better, I got better on the pitch too, because when you are playing one of the most important things is confidence
"It's good that I can speak Spanish with him on the pitch, but Gabby knows he needs to improve his English because that will make the football easier," Monreal told the matchday programme.
"Myself, Hector, everyone is helping him every day with it because it's much better for the team."
Monreal has been in fine form all season, and says mastering English played a big part in becoming accustomed to the demands of the Premier League.
"I know exactly how he feels, because it was the same for me when I first arrived,” he said. "When my English got better, I got better on the pitch too, because when you are playing one of the most important things is confidence.
"If you are confident in yourself, you feel better because you are more relaxed and you feel the authority to correct things you see. You feel more involved in the group."Copyright 2017 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source