France midfielder Lassana Diarra says his cousin was killed in the attacks in Paris on Friday.
"It is with a heavy heart that I heard this news," ex-Chelsea, Arsenal and Portsmouth player Diarra tweeted.
Several sporting fixtures in France were postponed after 129 people were killed in attacks across the capital.
Diarra, 30, was playing in the friendly against Germany at the Stade de France where three suicide bombers died in blasts outside the stadium.
Both teams spent the night in the stadium because it was deemed too risky to venture outside.
The French Football Federation (FFF) said Tuesday's international friendly against England at Wembley would go ahead following three days of national mourning.
Diarra, who plays for Marseille, added: "As you may have read, I was touched personally by the attacks.
"My cousin, Asta Diakite, was among the victims of one of the shootings, along with hundreds of other innocent French people. She was like a big sister to me.
"In this climate of terror, it is important for all of us who represent our country and its diversity to stay united against a horror which has no colour, no religion. Stand together for love, respect and peace.
"Thank you all for your messages, take care of yourselves and your loved ones, and may the victims rest in peace."
France striker Antoine Griezmann, who was on the pitch with Diarra when the attacks occurred, said his sister had a narrow escape from the Bataclan theatre, where 89 people were killed.
The 24-year-old Atletico Madrid forward said on social media: "Thanks to God that my sister was able to leave the Bataclan. All my prayers are with the victims and their families."