French side Bordeaux, then in Ligue 1, signed Klidje as a teenager from his homeland in 2020 but he made just five first team appearances.
Those games came in the French top-flight during the 2021-22 campaign, before Klidje moved to Luzern the following season.
He played 14 times in his first season in Switzerland but an injury curtailed his campaign.
The following year he managed four goals in 24 games, and kicked on again last term by adding 12 goals and three assists.
Klijde has also played 18 times for Togo, scoring twice.
“He adds extra pace and trickery to our front line and performed well for Luzern last season, and at 24 has a lot of room for development,” Gray said.
“We want to help him progress, and look forward to working with him moving forward.”
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