Tunisian international Ali Abdi on Thursday received the backing of his French club Nice amid a "barrage of threats" for joining his national team before the Ligue 1's side crucial play-off.
Nice said it had failed to reach agreement with the Tunisian Football Federation to allow the defender to compete in both play-off matches ahead of the World Cup.
Abdi played the first leg, a goalless draw against Saint-Etienne, but "was forced to travel to Tunisia to complete the administrative procedures related to his US visa and is determined to return to support the team for the second leg," Nice said in a statement.
"Between representing his club and fulfilling a call-up to the World Cup with his national team, the choice, both personally and professionally, was particularly difficult," Nice said.
"Faced with the onslaught of threats he is receiving on social media, the club calls on everyone to show restraint and respect towards a player who is a victim, just like the club, of these events."
Nice will attempt to preserve their top-flight status on Friday in the return leg at the Allianz Riviera, which will be played behind closed doors due to incidents caused by Nice supporters.
Saint-Etienne, who have been French champions 10 times in their history, are bidding for a quick return to the top flight after being relegated last season.
Tunisia open their World Cup campaign against Sweden on June 15 in Monterrey, Mexico. The group also includes Japan and the Netherlands.