Sion says Darragi will sign a four-year contract to move from African Champions League winner Esperance.
The 24-year-old Darragi also helped Tunisia reach the African Cup of Nations quarterfinals this month.
Sion says Darragi had been courted by Inter Milan, Marseille and Werder Bremen.
Sion faces a fight to retain its top-tier status for next season. It is appealing a 36-point deduction by the Swiss Football Association for taking legal disputes with UEFA and FIFA to civil courts.
The club is 16 points adrift in last place and faces a likely relegation playoff with a second-tier team.
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