Nurmagomedov submitted Gaethje in the second round before making his surprise announcement in Abu Dhabi
Manchester United and Chelsea played out a goalless draw at Old Trafford in a game that was bereft of quality and chances.
Cristiano Ronaldo is a doubt for the fixture after he tested positive for the coronavirus.
Former Man United star Darren Fletcher back at the club in coaching role
The Brazilian legend is widely regarded as one of the greatest footballers of all time and has been the subject of high praise from the trio
The Dutch midfielder has yet to appear in Solskjaer's first 11 in the Premier League since joining in a £40m summer move from Ajax