The American side will take on Belgium tomorrow for a place in the quarter-finals in Brazil.
Lukaku, who scored 16 goals during his loan stint with Howard's Everton last season, has failed to find the back of the net so far in his country's campaign.
"People have told me that Lukaku has had a difficult tournament," The Express quotes Howard as saying. "I have seen some of the games.
"Romelu was brilliant for us at Everton. He went through a spell when he wasn't scoring every game and then he caught fire again, so I wouldn't read too much into that."
Belgium won all three of their group games, while the USA head into tomorrow's clash on the back of one victory, one draw and a defeat.