PSG refused to let Brazil star Neymar return to Barcelona in the close season after the clubs failed to agree on a fee for the world's most expensive player.
Neymar upset supporters in Paris with his pleas to leave but a return of four goals in six Ligue 1 games amid injury troubles have helped prove his commitment to the cause.
Head coach Tuchel, however, admits it can be tough to keep the 27-year-old in line.
He told France Info: "[It's] not easy at all! He has a big, big heart, but unfortunately, he doesn't always show that he's a generous, reliable boy.
"Sometimes he's provocative and it's a great pity because it's not necessary."
"I tell him. We laugh a lot together and I always try to tell the truth," Tuchel continued.
"He accepts it, but it's hard. Ney is provocative when he feels something is wrong, but he isn't when he is calm."
PSG paid €222million to sign Neymar in 2017 with a view to him spearheading their bid for Champions League glory.
Successive last-16 exits have instead added to the doubt over his future along with that of Kylian Mbappe, who regards last season's European failure as a key reason he will not win the Ballon d'Or this year.
Real Madrid reportedly want the talented 20-year-old but Tuchel insists PSG cannot afford to lose either of their valuable attacking assets.
"He can definitely do better. He must and he can," the German said of Mbappe.
"He has the opportunity to win everything, individually and as a team. He's a key player for us. It's not possible to win anything without Ney or without Kylian.
"They are truly exceptional players. Really exceptional. Mbappe is super young. He has to protect himself and improve himself every day.
"He can win everything."
PSG face Madrid in the Champions League on Tuesday knowing a point will be enough to seal top spot in Group A.