Diarra remains part of the France squad that will face England in Tuesday's emotionally charged international friendly, where players and fans at Wembley will pay tribute to 129 people killed in a co-ordinated terrorist assault on the French capital on Friday.
In a statement released on Sunday, Marseille midfielder Diarra confirmed that his cousin Asta Diakite died as six locations across Paris, including the Stade de France as Les Bleus played Germany, were targeted.
The sister of Antoine Griezmann was in attendance at the Bataclan theatre, where 89 people were killed after gunmen stormed a concert by American rock band Eagles of Death Metal, but survived the attack.
Like Diarra, Griezmann remains in contention to face England and coach Deschamps told his pre-match news conference that their presence promoted unity and solidarity among the squad at this difficult time.
"Of course two of our squad have been profoundly touched by the terrible incidents," Deschamps told a press conference on Monday.
"On the one hand, Griezmann was fortunate enough to have a feeling of relief and happiness – the fact that his sister managed to stay alive in the incident that happened at the Bataclan concert.
"Lass unfortunately has been touched deeply by the loss of a relative who he was very, very close to.
"We've managed to stay together. I think that it's great that he's stayed with us.
"I've talked with both the lads, as I have with a lot of the players and I think that his presence has almost been a sense of reassurance for us.
"Lassana has been very strong. He, as we all have, has learnt the value of unity and solidarity.
"I can only repeat at this time the message that Lassana Diarra has put out on social media, the very strong message that sport knows no colour and knows no religion."
Diarra and Griezmann played 80 minutes of the 2-0 win over Germany that took place as the attacks unfolded - including three suicide bombers detonating explosive belts in the vicinity of the stadium - and Deschamps gave his account of the events.
"During the game we heard the loud noises, the explosions, but you are so focused on the game – you half wonder what that is without knowing what really happened," he said.
"We didn't realise until after the game the terrible disastrous event that had been taking place both in and around the stadium and in certain areas of Paris.
"When it became clear that Germany wanted to remain in the stadium, independently of what we were recommended by the French security services, I approached [coach] Joachim Low and the rest of my German counterparts and we said that we would remain with them.
"It was important to stay with them until the right solution, until the security for them, had been arrived at.
"We didn't get back to Clairefontaine [France's training base] until the small hours. We tried to eat something, we tried to sleep but I can reveal it was difficult to do either of those things.
"The night itself was very, very short before daybreak came around."
For much of the news conference, Deschamps repeated the assertion that sport can be a force for good and unity during such times of crisis and that representing his country at this moment was a particular source of pride.
The 1998 World Cup-winning captain added: "Throughout my entire career in the game, football has always had a very important function in everyday life.
Globally it had this very strong role in our society. Sport and football is a way of life in many different nations. It's also a strong symbol - players on and off the field can be great role models
"These values can be very, very important to never forget those values.
"We have the chance tomorrow to represent those very beautiful colours – blue, white and red - and we will do that with pride tomorrow night."