Villa are winless in their past two games and have slipped three points behind league leaders Liverpool.

"I would have thought because of how well they have done and because they are still competing in Europe, there’s an opportunity to bring players in and add to that squad," Kelly told BBC Radio 5 Live's Football Daily podcast.

"Emery is an intelligent manager and will want to bring in players that fit his system and style really well, bringing competition for places. That is always important if you are in Europe and pushing for Champions League football in the Premier League.

"The club have got to back him and allow him to bring in the right candidates to help strengthen."

Reflecting on what went wrong at Old Trafford, ESPN's senior writer Mark Ogden added: "They got complacent. They were so in control that I just think they took their foot off the pedal and allowed United to get back into it.

"They were caught by surprise by United’s intensity at the start of the second half because we have not seen that from United for a long time. Villa would have come out thinking 'we just need to keep control of the game and get another goal for this to be one of the most comfortable wins of the season'.

"But United just knocked Villa off their stride with their intensity and it was a collective thing in switching off. Villa now have picked up one point in two games over Christmas. They are still in the title race but have thrown away the chance to be top.

"There was no sign of that getting to their heads at half-time, so I think they just got a little bit complacent and thought it was easier than it was."