Manchester United boss Ole Gunnar Solskjaer could be heard shouting 'Marcus, he cannot defend!' as he encouraged his forward to attack Arsenal full back Cedric Soares.
Solskjaer shouted from his technical area as he willed Rashford to get at the Gunners defender, who is filling in for the injured Kieran Tierney on the left back.
The United boss yelled: 'Marcus, he cannot defend. He cannot defend. Take him on if you want.'
Arsenal have conceded two goals in the three Premier League games Cedric has played this season.