The Norwegian moved to Selhurst Park in January but has since failed to score a single goal for Palace.
He will stay with the Belgian club until the end of the season.
Eagles boss Roy Hodgson said of Sorloth earlier this week: "He's a much better player than he's been able to show in the games because we see his accuracy every day in training.
"But for goal-scorers and centre-forwards, confidence does play a big part."
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