Lukaku was an unused substitute as the Blues recorded a 2-0 victory against the French champions at Stamford Bridge.
Goals from Kai Havertz, who led the line superbly in Lukaku’s absence, and Christian Pulisic gave Chelsea the advantage going into the second leg in three weeks’ time.
Lukaku had just seven touches of the ball including one from kick off when Chelsea defeated Crystal Palace 1-0 over the weekend. His tally was the lowest recorded by a player to have completed the entire 90 minutes in a Premier League game.
Having come in for criticism for that output, Tuchel was keen to protect his much-maligned striker, who has scored just ten goals in 28 games since joining from Inter Milan for £97m last summer.
"It was not the moment after the match where everybody was focused on the few touches that we had to put him right into the next fire. It was the moment to take a step back. That was the decision and that's it," said Tuchel.
"You can clearly see we have a strong win and strong performance. It was a tough match and almost every question is about Romelu. The focus is huge. There were nine other players who did not play.
"We should never forget we consider this sport a team sport and the 11 guys who play do everything to commit fully to what we plan and commit fully to their team-mates. Those on the bench have to do the same and this is how it works.
"Especially at Chelsea and especially for us and this is how we win football matches."
