Lukaku, who left Chelsea as a youngster, joining Everton and Manchester United before moving to Italy, where he won the Serie A with Inter Milan, returned to Stamford on a £97.3 million deal last summer.
The Belgium international, who started brightly under Thomas Tuchel, has faded into a bit-part player in recent months, starting only two games against lower-league opponents.
Lukaku has lost his striker position to Kai Havertz and came off the bench in the 77th minute during the Blues' 2-0 FA Cup semi-final win over Crystal Palace on Sunday.
Ruben Loftus-Cheek and Mason Mount scored for Chelsea, who will now face Liverpool in the final at Wembley.
Lukaku had the opportunity to put his name on the score sheet but sent a glorious chance cannoning off the post.
And former Blues defender Melchiot thinks he needs to clear the air with Tuchel.
“He needs a good chat with his coach,” Melchiot told the talkSPORT Breakfast.
“To understand what his coach wants because if not he's just killing his own confidence.
“Coming back after an injury and getting back in the team and coming on, of course, he hit the post trying to get the ball in the goal, it's just sad, a player of his stature, of his ability.
“Coming with so much confidence and then going through the moments he's going through now, the only thing he can do for himself has a good chat, understand what the coach wants because I don't always think that Lukaku really understands what's expected from him in the system that Tuchel wants to play.”