Lukaku left Inter in August and returned to Chelsea for a second stint in a deal worth a club record £97.5 million ($131.46m).
"After two years in Italy, in which I worked a lot at Inter with trainers and nutritionists, I am physically fine. But I'm not happy with the situation, this is normal," Lukaku told Sky Italy.
"I think the coach has chosen to play with another system, I just have to not give up and continue to work and be a professional. I am not happy with the situation, but I am a worker and I must not give up."
Sky did not say when the interview took place and did not elaborate on the "situation," with the full interview set to air on Friday.
Lukaku has either led the line or played alongside a fellow striker this season at Chelsea but the Belgium international has missed nine games since October due to injury and COVID-19, scoring seven goals in all competitions but one in each of the last two matches.
Chelsea were top of the standings for several weeks but now find themselves in second place, eight points behind leaders Manchester City after two wins in their last six games.
Tuchel expressed his frustration at his side's injury crisis and some refereeing decisions on Wednesday after a 1-1 draw at home against Brighton & Hove Albion.
"It's too much, at some point it's too much," a visibly strained Tuchel told reporters after he saw wing-back Reece James hobble off with a hamstring injury before fellow defender Andreas Christensen went off at half time with a back problem.
"This is where we are and you need to adapt your demands to the situation you are in," he said. "We need a full squad over weeks and weeks, and then we can play much better."
Lukaku revived his career at Inter where he scored 64 goals in two seasons and won the Serie A title before his departure. The 28-year-old said he hoped to be reunited with the club in the future.
"I really hope in the depths of my heart to return to Inter, not at the end of my career, but at a still good level to hopefully win more," he said.
"I have always said that I have Inter in my heart, I will return to play there, I really hope so. I am in love with Italy."
Chelsea host Liverpool on Sunday with the Anfield club one point behind Tuchel's side with a game in hand.