Cape Town - Everton manager Ronald Koeman says he doesn't like the criticism aimed at Romelu Lukaku for his poor showing in the Merseyside derby defeat to Liverpool.
The Toffees were swept aside 3-1 in Saturday's clash at Anfield, where the Premier League's top scorer was unable to hit the target.
"Maybe some players didn't perform at the level that maybe they showed in the last few games," Koeman said ahead of Tuesday's trip to Old Trafford.
"Romelu, it was difficult. I spoke to Romelu, he was not really sharp, he was a little bit tired. That can all influence the performance of the player.
"But he's the top scorer of the league. Why now about the Liverpool game do we need to criticise Rom? He's a great striker, he's working hard.
"He's a human boy, it's not always a 10, that's football and if you don't play football, maybe you don't understand it."
Although Koeman insisted that he was happy with his team's performance against the Reds, he will be hoping for a better showing against Manchester United.
"We know that they have difficulties at home in the last few results," the Dutchman said of the Red Devils. "They are still a really strong team and we know some players will come back for them.
"We like to dominate the game but we know we need to defend at United."
Meanwhile Zlatan Ibrahimovic's return from suspension may be just the lift that Manchester United need as they attempt to improve their Premier League home form against Everton.
The former Paris Saint-Germain striker, United's leading scorer this season, has missed three domestic matches through suspension – in which time Jose Mourinho's team have been knocked out of the FA Cup and lost ground in the race for a top-four finish.
Kick off is at 21:00.