The 21-year-old's transfer fee could eventually rise to £3million and he has signed a four-year contract with the option of an extra year in the club's favour.
"He possesses outstanding physical attributes," Albion boss Tony Mowbray told his club's official website.
"We've brought in raw potential and there are parts of his game he needs to develop.
"But we're looking forward to helping him improve over the next few years, and hopefully seeing Leon play his part in the future success of the club."
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