He experienced several loan spells, including a season under current Blues boss Alex McLeish at Rangers, before leaving Liverpool to join Portsmouth on a free transfer in 2005.
But in hindsight the 28-year-old, now available for selection again after a hamstring problem, wishes he had been more patient on Merseyside.
Vignal said: "I should have stayed longer at Liverpool and been patient but, when you are young sometimes you don't realise things.
"I only played a few games at Liverpool, and when you are young, you want to play every game.
"I should have said 'Gregory, be patient, your time will come, you cannot play all the games'.
"When you get older, you realise that with extra experience because Liverpool are a massive club."
Vignal added: "Do I regret leaving? Yes. I should have never left Liverpool.
"After Rafael Benitez came in, I went on loan to Rangers but, when you play for a club like Liverpool, you realise how massive it is."
Vignal faces strong competition from for his left-back role after Liam Ridgewell's successful conversion from a central defender in recent games.
But Vignal, who is at St Andrew's in a season-long loan from Lens, is happy to be back working with McLeish and is a big fans of his motivational qualities.
He said: "I had played with the gaffer before at Rangers. He pushed me a lot.
"When you like and respect the manager, you want to give everything for him and he knows how to talk to me, how to push me. It's better for me because I know what he expects.
"He is very good psychologically with the players, very motivational, like he was at Rangers.
"People say the Scottish Premier League is easy because there are only two teams going for the title every season but that is wrong.
"You must win every game because, if you lose one, then it can cost you the league and every other team are hard to play against because they want to win against Celtic and Rangers.
"You have to find the motivation to get your players competitive every week in Scotland and that's what I like about the manager.
"He wants to be a winner every week and is so keen for Birmingham to do well."
Liverpool 1/3, Draw 4/1, Birmingham 8/1