Romelu Lukaku is suffering from the strain of his ever-present Premier League appearance record at Manchester United this season, according to manager Jose Mourinho.
Lukaku scored seven goals in as many Premier League matches in a flying start to his United career at the beginning of the current campaign.
The £75 million signing from Everton has since contributed only three more in 13 subsequent appearances, while his defensive errors from set-pieces proved costly during the recent 2-1 derby defeat to Manchester City and a 2-2 home draw against Burnley last time out.
Speaking at a news conference ahead of Saturday's match with Southampton, Mourinho suggesed the physical toil undertaken by Lukaku as United's only senior striker until Zlatan Ibrahimovic's recent return from injury has gone unappreciated.
"People don't have to be grateful to Romelu – I have to be," he said. "Not you [reporters], not the supporters, not the pundits – I have to be.
"Twenty matches in the Premier League, 90 minutes. For a striker, for any player, it is absolutely incredible.
"But if you are a central defender or a holding midfielder, if you are in a position where you can control your energy and your positional play, you can resist, you can survive.
"For a striker in the Premier League to play 20 matches, 90 minutes, I have to be very grateful for his personality and his character.
"Has he been unlucky in our box in recent matches? He was in the picture – it was not just him – but he was in the picture in some of the last goals we concede.
"Is it a consequence of a player who needs a little rest or just a consequence of the moment and the occasion?
"But the guy is fantastic for me and for the team and gives absolutely everything. I have no criticism."
Mourinho was then asked whether he would look to rest Lukaku and replied, "No. I can't."
"[Lukaku] is physically a monster but he is not a machine and I think he is feeling it."