Hickey missed the majority of last season with a hamstring injury which also kept him out of Scotland's Euro 2024 campaign.
As a result, the Scotland international has not played competitive football since featuring in a 2-0 victory over Chelsea in October 2023.
Hickey was working his way back to fitness after undergoing hamstring surgery in April, but Brentford have now revealed that the wing-back has suffered a fresh injury setback.
Brentford have confirmed that Hickey suffered a setback in training last week and has undergone another operation to resolve the issue.
Hickey set for extended spell on the sidelines
The Bees have stated that Hickey is now expected to miss the majority of the 2024-25 season, dealing a significant blow to Brentford boss Thomas Frank.
Brentford's head physio Nick Stubbings told the club's official website: "The procedure involved the removal of the previous repair sutures and making a new tendon repair.
"Now we aim to start afresh and help Aaron return to his previous level of health and performance."
Hickey's fresh injury blow will rule him out of international contention for a considerable period, including Scotland's upcoming UEFA Nations League fixtures against Poland and Portugal.
How will Hickey's absence affect Brentford?
Hickey's injury has deprived Brentford of some useful versatility, with the 22-year-old able to play on the left or right side of defence.
However, they have already learned to cope with Hickey's absence, having been without his services for over 10 months.
Frank can currently call upon Vitaly Janelt, Rico Henry, Kristoffer Ajer and Ryan Trevitt as his full-back options, but it is an area where they seem to lack real depth.
Having seen Hickey sidelined for a significant period, it remains to be seen whether Brentford will make an effort to sign a new full-back before Friday's transfer deadline.