The two teams have met six times in the competition with both sides winning two games a piece; however Francis believes the European champions have landed the 'ideal draw'.
"I think they will be delighted with this draw," he told Sky Sports News.
"The Portuguese league isn't the strongest league in Europe and Porto are currently four points clear of Sporting Lisbon, who if you remember were humiliated by Bayern Munich in the last round.
"I think it is an ideal draw for Manchester United. I watched Porto in their last-16 second leg tie against Atletico Madrid and they went through on the away goals rule after drawing 0-0 at home and it isn't a particularly hostile atmosphere.
"The crowd are a good way away from the playing surface, which is an excellent playing and surface, and that will obviously suit the passing skills of Manchester United."
FavouritesThe bookmakers have made Manchester United favourites for the competition after the draw and Francis, who scored the winning goal in Nottingham Forest's 1979 European Cup final triumph, believes only Barcelona can now trouble the English clubs.
"There are five teams in this final eight that can win this competition," he said. "I think from the start of the competition you looked at the four English teams and Barcelona, and there is no surprise that those five are through to the last eight.
"I can't see anyone outside of these five winning it and that includes Bayern Munich. Despite the fact they scored 12 goals over Sporting which was an outstanding tally over two legs, I don't think they are as strong as they have been in the past.
"They have some good players but Barcelona are an outstanding team and they are the big threat to the English teams without doubt."
Feel good factorThe last time Manchester United and Porto met in the Champions League was in 2004 when Jose Mourinho famously charged up the Old Trafford touchline as his Porto side knocked out Sir Alex Ferguson's men in the last-16.
Mourinho went on to lead his side to the final where they beat Monaco and Charlie Nicholas believes the memory of that night in Manchester will give the Porto players a boost.
"I think the feel good factor from the last time Mourinho took Porto through in dramatic fashion at Old Trafford will be in their minds and I think they will fancy it, because playing at Old Trafford first means they won't have to force a result.
"You think about teams like Villarreal who went to Old Trafford and stood firm this season and Porto will be looking to do the same thing. If they play nice and tight and get a draw or lose 1-0 then they will know exactly what they have got to do in the second leg.
"The only thing is that Manchester United have got so much variety and pace upfront that they could easily score away from home and that's the difficulty. But if Porto want to make it through they will have to get a result away from home. If they lose 2-0 the tie is over, that's how close it can be for them."