Mellor was recalled by the Red Devils after making only four appearances in all competitions for Salford.
He now looks set to join the League Two side on loan for the remainder of the campaign, with the forward completing a medical and paperwork being signed off in the next 24 hours.
The 21-year-old has also featured four times for United’s Under-23 team this season, netting three times and grabbing one assist.
Mellor has 25 minutes under his belt for the Red Devils’ first team, having come off the bench in their Europa League fixture with Astana in 2019.
Should he leave, Mellor will become the seventh player to leave Old Trafford on loan during the winter window, with Teden Mengi, Ethan Laird, Axel Tuanzebe, Anthony Martial, Amad and Reece Devine all departing.
Though predominantly a striker, the youngster can also operate on either wing as well as in the number-10 role.
Crawley currently sit 15th in League Two with 32 points from 15 games and have scored 29 goals so far - fewer than 15 other clubs in England’s fourth tier.
John Yems will be hoping Mellor can help bump that number up in the remaining few months of the season, should a deal be confirmed.