Basadien, one of Stellies' standout performers last season, earned a move to the champions after an impressive campaign.
But his time at Chloorkop has been marked by limited minutes and stiff competition, placing his AFCON hopes in jeopardy ahead of December's tournament in Morocco.
Barker says he feels a mixture of pride and concern.
"For me, when a player I've worked with moves on to a bigger club, it's usually a great sense of pride," he told Soccer Laduma.
"I've always been involved in development, even back in my Defence Force days. Seeing players grow and go on to improve their lives is incredibly satisfying. Watching guys like Bongani Khumalo, Andile Jali and Bongani Zungu become household names... those are proud moments."
But when a move doesn't immediately translate into regular game time, Barker admits a different emotion sets in.
"With Fawaaz, it becomes a little bit not nice," he said.
"I was very happy for him when he joined Sundowns because it's a big step up - competing for titles, playing against top talent. But when he doesn't play, you worry. You feel maybe if he had stayed, he'd be getting more minutes and his chances with the national team might be stronger."
Despite his concern, Barker remains optimistic about his former player's resilience.
"Fawaaz is talented, disciplined and hardworking. I know he'll keep pushing. But as a coach who's invested in his journey, you can't help but worry a bit when things don't go smoothly."
Ultimately, Barker says the pride remains - but so does the hope that Basadien's breakthrough at Sundowns will still come.
Stellenbosch defender Thabo Moloisane has expressed confidence that the club will soon rise out of their slump, despite their current position near the relegation zone in the Betway Premiership.
Nuno Santos has wasted no time embracing the high standards and relentless ambition that define Mamelodi Sundowns, and the Portuguese midfielder believes his mentality is a perfect match for the reigning Premiership champions.
Orbit College will look to strengthen their foothold in the Betway Premiership when they host a struggling Stellenbosch FC at Olympia Park Stadium on Wednesday.
Mamelodi Sundowns' midfield has been bolstered by the arrival of Portuguese international Nuno Santos, who completed his move from Vitoria SC in August.
