Out for much of the season with injuries and with a damaged reputation following a disastrous World Cup, Lukaku has slowly worked his way back to his best.
The Belgium striker has scored five times and set up three more in his last six matches and his double in Saturday's 4-2 win over Sassuolo highlighted his new-found confidence.
Lukaku celebrated his 30th birthday by beginning and ending the scoring at San Siro, spinning and lashing home the opener from the edge of the box shortly before half-time and drilling in his eighth league goal of the season just before the end.
A striker in his sort of form should probably expect to be starting such a huge match on Tuesday, where Inter defend a 2-0 first-leg lead in a bid to reach their first Champions League final since the last time they won it under Jose Mourinho (60) 13 years ago.
However it will likely be veteran Edin Dzeko (37) who partners Lautaro Martinez (25) up front for the second of two huge derbies with Milan, with Lukaku set to come on as an impact substitute.
"Of course every player wants to start, but the coach has to make his choices for the team," said Lukaku
"As I have always said, the most important thing is Inter and that's why I give my all for the team."
Inter CEO Beppe Marotta said on Saturday that there was a chance of loanee Lukaku staying at Inter next season but with parent club Chelsea yet to announce their new manager his future remains uncertain.
What is sure is that the San Siro will again be a riot of colour and noise as two of Italy's standard bearers recreate the days when they were among Europe's elite.
Inter fans have good reason to be confident about their side's chances, as they have a healthy lead from the first leg and are bang in form.
Heads bowed
Simone Inzaghi's side have won seven matches in a row, scoring 20 goals in the process and playing with a confidence which has been lacking for most of an odd league season in which they have lost 11 times, more than any other team in Serie A's European places.
Milan meanwhile come into Tuesday's match in disarray after an embarrassing defeat at lowly Spezia which ended with team and coach Stefano Pioli (57) having a post-match discussion with their away support.
Pioli and his players had their heads bowed in remorse while Milan's hardcore ultras bellowed encouragement in the hope that their words might add something which was missing in the first leg.
However seeing as the big miss in the first leg was Rafael Leao (23), the Portugal winger's probable return on Tuesday from a thigh injury will be much more of a boost to Milan.
Leao has been crucial to Milan's advance to the last four for the first time since 2007 and without him last week the seven-time European champions were painfully short of cutting edge.
"We're playing a match which could make history for us, we need to believe that we can beat Inter," said Pioli on Saturday.
"We haven't been good enough in our last two matches, but we can play much better."
