The Gunners are believed to be determined to sign a new central midfielder before the end of the transfer window but have thus far found it difficult to agree a deal for either of their main targets.
However, according to The Athletic, Mikel Arteta's side are ready to drop their interest in Aouar in order to ensure that they wrap up a deal for Thomas before the deadline at the start of October.
The Ghana international has a £45m release clause in his current deal at the Wanda Metropolitano, which is due to run until the summer of 2023.
Thomas was again a key player for Diego Simeone's side during the 2019-20 campaign, making 46 appearances in all competitions, contributing four goals and one assist.
Arsenal will be looking to make it three Premier League wins in a row at the start of the new season when they welcome champions Liverpool to the Emirates Stadium on Monday night.