Griezmann has been scrutinised for his form for much of the past 15 months since he completed a €120million move from Atletico Madrid to Barca.
The 29-year-old has not looked fully at ease in the Catalans' forward line, his last goal in LaLiga – one of only nine he scored last season – coming in the 4-1 win at Villarreal on July 5.
Griezmann, who got a goal in the 7-1 friendly thrashing of Ukraine, also scored in the 4-2 Nations League win over Croatia but, ahead of Wednesday's rematch in Zagreb, he again finds himself facing accusations of poor form for the national team.
In the 0-0 draw with Portugal on Sunday, Griezmann, playing as a number 10 behind Olivier Giroud and Kylian Mbappe, managed just two shots and created one chance for team-mates.
However, he did attempt 55 passes in the opposition half – the most of any player on the pitch – and highlighted his importance without the ball, winning back possession a game-high 11 times.
It is that kind of quality that Lloris believes will always be important, even if Griezmann's goal output is presently reduced.
"You can't question a player like Antoine Griezmann because of all he has done and all he has brought to France in recent years," the Tottenham goalkeeper told reporters on Tuesday.
"All players have ups and downs. There are times when you succeed more than others. He is currently going through a slightly complicated period in attack, but above all, I see a player who is ready to defend and make the effort for his team-mates. There is no question about that.
"We have to keep our backs to the wall and help him, too. He has our full confidence. We know he has the ability to make the difference in truly important moments for France.
"Let's be patient but, in any case, France can only be strong if we are all united and not pointing the finger at any individual player."
Lloris is looking forward to Wednesday's game at Stadion Maksimir, at which a number of fans will be permitted.
"The presence of supporters is of course good news," he added. "There will inevitably be a bit of hostility but, for the French players, it's a good thing to be able to overcome adversity to win this match.
"That's our goal, in any case. We'll give everything to give the right performance to win."