Arsenal strengthened its defense with the signing of Andre Santos from Turkish champion Fenerbahce on Wednesday and Per Mertesacker set to join him in north London.
Brazil left back Santos signed a long-term deal on the final day of the summer transfer window.
"Santos is a quality player, with the ability to both defend well and get forward and help with attacks," Arsenal manager Arsene Wenger said. "He has experience in the Champions League and for Brazil and has proven he can deliver at the highest level."
The 28-year-old Santos is joining a team that has collected just one point from its first three league matches, including an 8-2 rout by Manchester United on Sunday.
"It was one of my dreams to play for a major European football club and I have accomplished this," Santos said. "I am very happy to be part of this team. All the Brazilians who came to this club spoke wonders about it and I am delighted to be part of the Arsenal family."
Arsenal is also completing a deal with Werder Bremen for Germany defender Mertesacker.