Manchester United striker Romelu Lukaku has been unfairly criticised for his performances this season, Belgium boss Roberto Martinez says.

The 25-year-old has only managed six goals in all competitions in 2018-19 and was not always guaranteed a regular starting spot during former manager Jose Mourinho's final few weeks in charge.

Ole Gunnar Solskjaer oversaw a 5-1 thrashing of Cardiff City on Saturday in his first match as caretaker boss, but Lukaku was absent after missing training in the build-up to the trip to Wales.

Despite his struggles at club level, Lukaku is a key part of Martinez's Belgium side, scoring 14 goals in as many games in 2018.

And the former Everton boss thinks the scrutiny on the striker's scoring record for United is often unfairly used against him.

"There is a negative way of assessing Romelu's performance for Manchester United," he told The Sunday Times.

"When Rom scores, everyone expects him to score, and when he doesn't, he is almost directly the reason United haven't won.

"But Rom is ready for that challenge. He will never hide away. He understands what is expected of him.

"For Belgium, he has shown he's one of the best number nines in the world and I don't understand why he's being treated in a manner which he doesn't deserve."