The player himself insists he “hates” being labelled a target man.
Whatever the reason, something is not right with the striker who blasted Inter Milan to the Serie A title last season and was considered the final piece of the jigsaw when returning to Chelsea in the summer.
A run of six games without a goal is his longest barren spell since his miserable final season at Manchester United, which saw him fail to score in his final eight appearances for the club.
His present situation is nothing like as desperate as that, with mitigating factors outlined above, but Lukaku’s flying start has been brought down to earth.
Against Brentford on Saturday night, he was taken off after 76 minutes having failed to register a single shot on target – and only one shot of any description throughout the match.
Those statistics raise questions about the quality of service being delivered to a man who scored 64 goals in 95 appearances for Inter.
It also places the spotlight on Tuchel’s system, which continues to prioritise a stubborn rearguard over a free-flowing attack.
If Lukaku, who scored four in as many games upon his return to Stamford Bridge, is struggling at the point of a Chelsea team that has scored one or fewer goals in six of its 11 matches so far this season, he is in good company, with Tammy Abraham, Olivier Giroud, Timo Werner and Kai Havertz all suffering at various times under Tuchel.
It is not that the German is overly negative in his approach, just that a three-man defence with two holding midfielders has been the platform for his success at Chelsea and one he seems reluctant to abandon.
“Does it have less value that we are a difficult team to play against than being a team that always scores an easy three goals?” asked Tuchel ahead of Wednesday’s Champions League tie with Malmo.
“Of course we can take this step when we are fully convinced and when it’s the moment to put more offensive players in, but it’s also about balance. This game is about balance and we found a balance.
“I think we can create chances in any kind of structure, but yes, of course we think about everything. But you have to find the right moment.
“We can also score from counterattacks, from ball wins. It is not only about creating chances against an opponent who’s defending deep – and a lot of teams are defending deep at the moment against us.
“It’s maybe the most difficult. We are looking for solutions. It’s why we are here. One solution could be to change formation and put in more offensive players. Let’s see.”
Malmo could be the ideal opportunity for Tuchel to let his players off the leash. A double-header against the Swedish champions has the potential to put Chelsea on course for qualification to the knockout stages of the Champions League after defeat to Juventus in their last Group H game.
It is also a chance to get Lukaku back among the goals, but Tuchel admits he is unsure about whether to ask him to play through his current struggles.
“In the very moment I feel Romelu a bit overplayed,” he said. “I think he played too many competitions over the summer, too many competitions with the national team. And now he has played the Nations League.
“He is a fantastic athlete and such a competitive guy that he digs in deep, he wants to win these things and he never takes it easy.
“I feel him a bit mentally tired. Not hugely that we have concern, but for me he does not fully enjoy without having second or third thoughts, for me he is overplayed and this is the key point.
“Once he finds his rhythm and things a bit easier, he will be fine but it is hard to judge if he really needs a break or if we need to keep him on the pitch.”