On January 6, 2017, United Soccer League side FC Cincinnati announced that they had signed Walker for their 2017 season. In a quote on the club's website, head coach John Harkes said, "We were impressed by Aaron during the Open Tryout last month and we feel are pleased that we have a player coming from our tryout for the second straight year. We think he will be a good fit."[2] However, John Harkes was fired by the club on February 17, 2017, and Walker ultimately saw no playing time in competitive matches during the 2017 season. On October 25, the club announced they had not exercised their option to keep Walker for the 2018 season.[3]
In February 2019, Walker, as well as his former FC Cincinnati teammate Dallas Jaye, signed with Greenville Triumph SC in the third-tier professional league USL League One. The two were reunited with their former coach John Harkes, who was serving as the head coach and sporting director for Greenville Triumph.[4] Walker re-signed with Greenville on January 11, 2022.[5]