Duff, 47, has been out of management since stepping down from Shelbourne during the 2025 season, having guided the Dublin club to the League of Ireland Premier Division title the previous year. It was the highlight of a managerial career that also included coaching roles with the Republic of Ireland national team and Celtic.
The former winger has not been involved in English football since leaving Fulham in 2014. He spent four years at the club after a two-season stint at Blackburn Rovers and his most celebrated spell at Chelsea, where he won back-to-back Premier League titles under Jose Mourinho.
Andrews, a close friend and former Ireland international teammate, gave Duff open access to Brentford's operation for three to four days as the 47-year-old assessed his options.
"It was amazing to see such a well-run club," Duff said. "Brilliant people, honest people, energy, enthusiasm, obviously real quality. It was so refreshing. The minute I walked into the building, I just thought to myself, wow."
He contrasted the experience with two of his former employers, making no attempt to soften his words.
"You look at maybe a couple of my ex-clubs — Blackburn, Chelsea — they're two basket cases and that's why they are where they are. Brentford, brilliant from top to bottom."
Andrews was careful to frame the visit as personal rather than professional, saying it was the kind of open-door access the club extends to visitors and declining to be drawn on whether Duff might join his staff.
"He's clearly a talented head coach. Exactly where Damien goes next, I don't know. He's a very unique individual that has undoubtedly got a lot of qualities as a coach."
Duff acknowledged he has no concrete plan but accepted that staying in Ireland may not be realistic given the limited number of roles available there.
"I have to start probably looking outside the country because there's not a big industry here. I belong on the grass. And whether it be here, the UK or somewhere else, I don't know."
Brentford are in contention for European football this season under Andrews, who took charge following Thomas Frank's departure for Tottenham Hotspur.