The teenage midfielder has been the subject of months of speculation regarding his future, having spent the majority of the current season on the bench.
That lack of regular minutes led to reports that Mainoo could be allowed to leave during the January window, either permanently or on loan, in order to gain more first-team experience. Napoli were among the clubs previously linked with a potential move.
However, United's stance appears to have softened after the departure of head coach Amorim last week. Amorim's exit has prompted renewed uncertainty around several players, but it has also sparked rumours that Mainoo is no longer expected to leave before the February 2 transfer deadline.
Darren Fletcher has since been placed in charge as interim manager, while the club considers a short-term caretaker appointment.
Ole Gunnar Solskjaer and Michael Carrick have both been linked with a temporary return until the end of the season, with Carrick understood to be leading the race and close to agreeing a deal.
That managerial upheaval is believed to have influenced United's thinking on Mainoo. Transfer expert Gianluca Di Marzio has suggested that the club may now be reluctant to part ways with the midfielder this month, despite earlier loan discussions.
"I think things will change for Kobbie Mainoo after this," Di Marzio told AceOdds.com.
"I hope Man Utd make another mistake like they did with [Scott] McTominay and [Rasmus] Hojlund. Players that were not performing at Man Utd are top performers at other teams. It's good for us in Italy and Napoli.
"In Italy, we say, 'there is no two without three'. So obviously Napoli said after McTominay and Hojlund, we'll try to get Mainoo too.
"With a new coach I don't think they'll try to sell Mainoo and will try to give him more minutes."
Juventus manager Luciano Spalletti praised his team's effort after a 5‑0 win over Cremonese at the Allianz Stadium on Monday but insisted they are still not on the same level as Inter Milan or Napoli.
Brighton boss Fabian Hurzeler praised his side after they knocked managerless Manchester United out of the FA Cup with a 2-1 victory at Old Trafford, sealing a landmark win in the competition.
Antonio Conte was sent off after a furious reaction to a VAR penalty decision, but Napoli responded with courage and quality to earn a 2-2 draw against Inter Milan at San Siro, with Scott McTominay scoring twice to rescue a point.
Darren Fletcher did not hide his frustration after Manchester United were knocked out of the FA Cup, with the caretaker boss hitting out at the referee following a damaging 2-1 defeat by Brighton at Old Trafford on Sunday.
