Lukaku managed only seven touches of the ball as Chelsea beat Crystal Palace last time out, a record low in the Premier League for a player who completed the whole match.
Re-signing for the Blues in the summer of 2021, Lukaku became Chelsea's record transfer in a £97.3million move from Inter Milan, and got off to a flying start.
Four goals in four games suggested the Belgian may be the solution to Chelsea's long-term striker issues, but just five goals in his following 23 matches have followed.
The 28-year-old also conducted an ill-advised interview with Sky Italia in which he expressed his regret at leaving Inter, riling everyone at Stamford Bridge.
Despite scoring in Chelsea's Club World Cup final win over Palmeiras, Lukaku again performed well below expectations against Palace, and Tuchel has now come to his defence.
Speaking ahead of the game, Tuchel said: "He's in the spotlight and we'll protect him. Romelu will always be part of the solution.
"Sometimes it's like this with strikers if they struggle a little bit with self-confidence and to find the space to get involved with a good defensive side.
"Of course it's not what we want and what Romelu wants but it's also not the time to laugh about him and make jokes about him."