Paul Scholes is worried about Kobbie Mainoo's legs and his inability to finish 90 minutes.
Mainoo came back into the Manchester United starting line-up for Sunday's 2-2 draw with Liverpool but was taken off after 72 minutes.
It means the 19-year-old has only completed the full 90 minutes once in United's last five Premier League games under Ruben Amorim.
And it strikes a marked contrast with last season, when the central midfielder regularly closed out full matches under Erik ten Hag.
Amorim's two-man midfield demands players bursting with energy and pundits fear he may struggle to live up to the expectations.