Griezmann, a €120million signing from Atletico Madrid in the transfer window, has struggled to find top form since moving to Camp Nou.
The 28-year-old has scored three goals in seven LaLiga appearances but has generally found it difficult to influence games from the left of Ernesto Valverde's attack.
He was dropped to the bench for compatriot Ousmane Dembele for Barca's latest game, a 4-0 league win over Sevilla on Sunday, in which Dembele scored.
There have also been concerns Griezmann is not suited to playing alongside club captain Lionel Messi, largely after the France forward admitted in a news conference that the pair do not often speak.
However, Lenglet insists there is no cause for concern around Griezmann's place at the club.
When asked if Griezmann is happier in the France squad than with Barca, Lenglet replied: "No. I am with him every day and I can tell you that he is very happy in Barcelona.
"He's a positive person who always has a smile on his face. When he arrives in the French team that fact doesn't change. He loves to make jokes, you know him. He hasn't changed, whether it's in Barcelona or in the France squad.
"He's someone who has just arrived and Barcelona is a different club from the other clubs, which plays a different game - a different game from Atletico.
"He has scored three goals, I think he's the club's second-best scorer, even though it's only the beginning of the season. It's still something quite positive.
"He works a lot for the team. He used to play as second striker at Atletico and now he plays on one side. He helps us a lot with his talent and his defensive efforts in every game. He's sacrificing himself for the team. I don't think there is an 'Antoine Griezmann case' as you can try to make me say."
Messi scored his first goal of the season from a free-kick against Sevilla, having been sidelined for much of the early part of the season with a calf problem.
Lenglet says the Argentina star has still been teaching him a few lessons in training, however, where he gives his defensive team-mates a torrid time.
"He is an extraordinary player. We are very happy to have him in Barcelona. He makes a lot of difference," said Lenglet.
"When we are in training, we set the pace. Leo often plays as a joker. He is very clever in his placement, in his way of protecting the ball. It's hard to steal it. You have to anticipate well in advance. We suffer daily but we are happy to have him with us every weekend. That's the main thing."
One of the big positives of Barca's season has been the breakthrough of Ansu Fati, the 16-year-old who has scored twice in five league appearances and captured the attention of Spain with his performances.
"Ansu is very talented," said Lenglet. "He's in a dressing room with a lot of international players and very good players in his position. He took advantage of some absences to have playing time. He was very good when he played.
"He has some minor problems given his age to follow the rhythm of matches and training, but he is very well cared for. He is very professional. It's a very pleasant surprise. I think he's a good player for the future but also for the present because he has many qualities."