Lukaku joined the Blues for a club record for of £97.5million in the summer and hit the ground running at Stamford Bridge.
He netted four goals in his opening four games, but they have dried up since then.
The last time he has scored for Chelsea was on September 14, against Zenit in the Champions League, and that was six games ago.
The 28-year-old has already played 13 times for club and country this season.
And, speaking ahead of Wednesday's Champions League clash against Malmo at Stamford Bridge, Tuchel admitted he is not happy about the demands placed on his star man.
The Blues boss said: "In my opinion, I feel Romelu overplayed.
"I think he played too many competitions over the summer and now he played Nations League.
"He is a fantastic athlete, a competitive guy and he wants to be out there and win, digging deep."
Tuchel went further to bemoan the amount of games footballers play these days, as the latest manager to take aim at the packed fixture schedule.
He added: "We lack a little bit of form and enthusiasm in the last per cent and one big reason is we play too much. Not as a club but the players.
"This is the situation right now. This is nothing new and the next national break is coming soon, it will not change.
"We have another competition in January/February. The Premier League is the toughest league in the world, there is also no shame in having a tight match against Brentford or a late winner against Southampton.
"We lack a bit of freshness, a bit of joy. We are coming from travels and games.
"If you travel through time zones, in a hotel, the you change that, one day at home, see family then back to the hotel, then at Brentford, then the Champions League, it can be tiring."