Ricky Sbragia's side will compete with Derby County, PSV Eindhoven and Paris Saint-Germain in a bid to reach the knockout stages, with the three ties scheduled to be completed by 21 December. The squad has returned from a training camp in Austria as preparations continue for the new season.
In last year's competition, United won the group before going out to Villarreal in the quarter-finals. James Wilson was overall joint-top scorer with five goals as Swansea City, Athletic Club and Celtic were all defeated.
Porto retained the trophy in 2017/18, after beating Arsenal in the final, following victory over Sunderland in the previous campaign.