Erik ten Hag admitted it wasn't the plan for Christian Eriksen to mark Erling Haaland for Man City's first goal in their 6-3 drubbing.
Haaland rose to nod in direct from a corner in the 34th minute with Raphael Varane off the pitch after receiving treatment for an apparent ankle injury.
United playmaker Eriksen appeared to be tasked with handling Haaland but he was effortlessly brushed off by the Norwegian and City scored twice more to take a 4-0 half-time lead.