The 18-year-old Ruiz, who scored three goals at the Under-20 World Cup in Colombia last year, joins from Costa Rica club Deportivo Saprissa.
Lille also signed French striker Nolan Roux from Stade Brest earlier this week amid media speculation that Moussa Sow, who is at the Africa Cup of Nations with Senegal, is about to leave for Fenerbahce of Turkey.
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