Brown, 19, made his WBA debut in May 2013, becoming the second youngest player in Premier League history when he came off the bench at just 16 years and 117 days.
However the winger left the Hawthorns months later, signing a contract with Chelsea. He has gone on to enjoy success with the club's youth sides, winning the FA Youth Cup twice as well as the Uefa Youth League.
After a handful appearances on the bench, Brown made his Blues debut against former club West Brom in May 2015 after Chelsea had already wrapped up the Premier League title under Jose Mourinho. He is yet to make another appearance for the first-team, however, joining Dutch side Vitesse Arnhem last season and linking up with Rotherham United this term.
Since leaving the Baggies, Brown has played just 11 minutes of first-team football in three years and Hopcroft still rues the loss of a player he describes as "the one that got away."
"It might turn out a correct decision. At the moment, it doesn't look a great decision," Hopcroft told BBC WM.
"I absolutely loved Izzy Brown. I thought he was the best of all the players that have left here. He could have gone on to play a similar number of games as Saido Berahino. He could have made his 100th appearance for West Brom and be in a better position than he is now.
"For whatever reason he chose not to go down that route. He chose to go down another route with a bigger club. He made a decision and his parents made a decision that West Brom wasn't for them at that time. I wasn't party to it, but I know really good offers were made."