Ardiles admits he still regrets leaving the Baggies for Tottenham and told the Birmingham Mail: "It's up to Tony Mowbray what he does but I speak from experience.
"It was the most difficult decision I made as a manager, possibly during my career.
"I didn't sleep during the night, I couldn't focus or concentrate on anything. It was a much harder decision than many people thought at the time.
"We had just been promoted and I was walking away from a club which I had a lot of affection for.
"Tottenham was my club. It was my dream. But it turned out to be my wrong decision."