Arsenal's Per Mertesacker has backed teammate Calum Chambers to become one of the best defenders in the Premier League.
The 20-year-old moved to the Gunners from Southampton last season and enjoyed a strong start to the campaign before Laurent Koscielny and Mertesacker came back into the starting lineup.
Gabriel Paulista's arrival has pushed Chambers down the pecking order this season, limiting him to just three appearances, but the German is adamant that the England international still has the ability to become one of the best at his position in the division.
"He's a good guy and we challenge each other every single day in training," Mertesacker told the club's official website. "That's what it's all about. He's eager to learn, he really fancies challenging every single centre-back and that's something you need.
"When you step up as a young talent, you need to challenge the old lads. It's really good to have him so that we can improve.
"You never stop working, you never stop doing things because there's someone behind you - in a respectful way - who is giving absolutely everything in every single training session. That's what my feeling is. When he does that, he's got a great chance to develop as one of the top centre-backs."
Chambers has been capped three times by the senior England team.
