Arsenal are considering Omer Toprak of Bayer Leverkusen and Simon Kjaer of Fenerbahce as they look to sign a new centre-half, Sky sources understand.
Gunners boss Arsene Wenger remains determined to strengthen his back-four following injuries to Per Mertesacker and Gabriel, and their chief target is Valencia's Shkodran Mustafi.
Sky sources understand German international Mustafi has agreed to join the Gunners as discussions continue over a fee between the clubs, but Toprak and Kjaer are among the alternatives.
Toprak is a 27-year-old Turkey international with 23 caps, who joined Bayer Leverkusen from Freiburg in 2011.
Kjaer is a 27-year-old Denmark international with 59 caps, who signed for Fenerbahce from Lille in 2015.
Wenger has been heavily criticised following Arsenal's 4-3 defeat at home to Liverpool in their opening game of the season, especially over a perceived lack of spending in the transfer market.
Wenger admitted after the defeat that his side were not physically ready for the clash, while he started young defenders Rob Holding - a summer signing from Bolton - and Calum Chambers together at centre-back.
The Gunners also want to sign a striker before the August 31 deadline, and target Alexandre Lacazette said on Monday he is open to a move.