Ronaldo, who was at United between 2003 and 2009, joined Juve for £99.2m in July after nine years at Real Madrid.
Their problems are such right now that any opposition might have represented a real challenge, but a group of the formidable Juventus, a returning Ronaldo, a revived, canny Valencia and awkward Young Boys is particularly fierce.
"It's a very tough group but the most important thing for us is that we have managed to get into the group stage and compete at this level", Red Star president Svetozar Mijailovic told reporters.
The only other group that at least poses the plausible prospect of a footballing powerhouse going out is Group A, featuring Atletico, Borussia Dortmund and Monaco.
Barcelona head a tough-looking Group B with Tottenham, plus former champions PSV Eindhoven and Inter Milan, while three more former European champions Bayern Munich, Benfica, Ajax are together with underdog AEK Athens in Group E.
Suspected asylum seekers rounded up in Qld
An illegal fishing boat has run aground and been found abandoned in crocodile-infested waters in northern Queensland, Australia. The department did not respond to questions of whether the vessel was carrying asylum-seekers, illegal migrants or fishermen.
Liverpool's consolation prize of Group C however still offers an opening-day visit of glamour club PSG to Anfield, complete with superstars Neymar and Kylian Mbappe.
With Lokomotiv Moscow coming out of Pot 1, Porto out of Pot 2 and Schalke out of Pot 3 you can safely deduce that all the teams remaining in Pot 4 would be desperate for Diego Forlan to call out their name. Real Madrid's all-time leading scorer will also make his return to Spain as Juventus are also scheduled to face La Liga club Valencia.
Here's our winners and losers list from the group stage draw.
The first round of group games will be played on September 18 and 19, with the last matches on December 11 and 12.
There were 13 former champions in a draw that included three teams Hoffenheim, Red Star and Young Boys making their group-stage debuts in the 27-season Champions League era.
Croatia worldwide midfielder Luka Modric - a Champions League victor with his club and World Cup finalist with his country - won both the midfielder of the year and overall best player awards.