Rob Holding also made his long-awaited return to action on Tuesday and getting a host of defenders back at once could help Emery steer what has so far been an inconsistent season back on track.
"I think no [he won't be ready to start against Manchester United]".
"I think no. Maybe in his mind yes, but we need to listen to the doctor and the doctor wants to do it progressively".
Rob Holding marked his comeback from a knee problem that kept him out for almost 10 months with a thumping header to put Arsenal 2-0 up.
Tierney played 77 minutes before being replaced by Hector Bellerin.
He said: "It was an opportunity for different players to take confidence, to take minutes". Firstly, the clear lack of one out-and-out leader speaks volumes of the squad's character, as the qualities of a captain are all about leading by example and taking the flak when things go wrong - something this crop of players fail to do.
"The muse is to present them minutes if we can", acknowledged Emery.
"Martinelli is a very young player but he came here and we were waiting and watching him, how he could improve with us", said Emery. "He played very well in pre-season, he was working each training with a big spirit and performance". If I get it, I will be more than happy.
"We are going to use him with Ainsley and Calum Chambers to help us in this position".
Forest, backed by nearly 8,400 fans, managed only one attempt on target in 90 minutes in their first visit to Arsenal since a 2-1 top-flight loss in August 1998.
Maitland-Niles picked up a red card during Arsenal's last Premier League clash vs Villa and now that Hector Bellerin too has been ruled out then we believe it would be Callum Chambers who would start at right-back in the Man United vs Arsenal game.
"Congratulations to Arsenal and good luck for the rest of this competition".