Sanchez wasted no time having a positive impact on the Manchester United team following his two assists in their comfortable fourth round win against the League Two side.
"He was cheap wasn't he?"
"I think we can be optimistic for the rest of the season".
"What I really like from him is the way he fights when the team loses the ball", said Herrera.
"We have a good group of attacking players you could see today we played with three of them, [Jesse] Lingard was on the bench, [Romelu] Lukaku was on the bench, Zlatan [Ibrahimovic] at home, [Anthony] Martial at home".
"We are creating the conditions for a brilliant and successful future for Manchester United". So we have a good group.
Sanchez was in the process of completing his transfer and Gunners boss Arsene Wenger admitted that Arsenal were culpable.
"I think Arsenal were very honest in the way they approached the situation", said Mourinho, of Sanchez's missed drugs test.
"Nobody knew where he was going to be, it was just a period of his transfer".
Yeovil boss Darren Way said Sanchez was "absolutely world-class" and added: "It's a total honour for us to go up against a side of that quality and a player of that calibre". But I think everyone understands that no-one knew where he was going to be, where he was going to train, where he was going to sleep.