Lukaku scored an excellent header to help United to a 2-1 win at the Hawthorns, though United remain 11 points behind leaders and fierce rivals Manchester City.
The Belgum international merely stood facing the crowd after his goal, as he did after scoring against Bournemouth in a 1-0 win.
And Phil Johnson, a sports psychologist, told Betstars that Lukaku is showing a lack of respect to his fellow United players.
"Romelu Lukaku's behaviour is reflecting Jose Mourinho," he said. "I know the Belgium management team.
"Lukaku is a young guy, like Anthony Martial, who needs support. If he played for Pep Guardiola, he would have a totally different relationship where he would receive a different style of support than what he gets from Mourinho.
"Lukaku needs the ball to score. Look at Radamel Falcao when he went to United and he only scored a couple of goals, then comes back to Monaco and he's top scorer. At Everton they played to Lukaku's strengths, but they aren't doing that at United, despite his good start.
"I think for Lukaku not to celebrate is disrespectful to his teammates, to himself and it reflects his manager's approach."