The Daily Star says United chiefs fear the demands of his young kids, Kai, four, and 11-month old Klay mean he may not be getting enough sleep.
The club, whose ground Old Trafford is dubbed the Theatre of Dreams, have now put him in a specially designed sleep centre.
United have built a state-of-the art sleep facility at the Aon Training Complex which has eight "quiet rooms" where players can snooze after training, and includes a cinema and a lounge.
Head of fitness Tony Strudwick is monitoring the striker, 28. He said: "You find that players who have young children get a slightly lower quality of sleep when those children are very young and that can affect performance.
"We have an extensive monitoring and recording process in place."
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