Msakni, who has earned 39 caps for Tunisia, was injured during a Qatar Stars League [QSL] match on Sunday against Al Sailiya that saw his team Al Duhail emerge 5-2 victorious.
In an statement released by Al Duhail, they announced: ''Msakni suffered a cruciate ligament injury.'' Whilst the player confirmed the injury on social media.
He wrote: ''Thank God for this [Al Duhail's sixth QSL title] but it's just fate to experience the unexpected. Congratulations for the trophy. Sadly this injury has denied me the chance to continue with my club and to play in the World Cup.''
Tunisia will first face England in the group stages of the World Cup, followed by Belgium and Panama. Msakni's absence will no doubt be a massive blow to the national team in their World Cup bid.