The 17-year-old signed for Burnley from Royal Racinh FC Montegnee in the January transfer window, but there have been delays over his international clearance.
Lazaar has signed a contract that will keep him at the club until the end of next season, but will sign professional forms before the end of this season.
Lazaar told Sky Sports: “I’ve really enjoyed English football so far and Burnley have made me feel very welcome and at home.
“I’m just looking forward to playing competitive matches for Burnley and hopefully returning to the Belgium team as soon as possible.”
