Ronaldo's summer has been overshadowed by accusations of tax evasion in Spain, which led to him being charged in a court.
Ronaldo's summer has been overshadowed by accusations of tax evasion in Spain, which led to him being charged in a court near Madrid last week, while he was handed an extended summer break by his club after playing for Portugal at the Confederations Cup.
He only returned to training at the weekend, meaning it would be a major surprise if coach Zinedine Zidane were to include the 32-year-old against his former club in the match at the Philip II Arena in the Macedonian capital.
"He needed to rest. He has had his holidays and that was important," said Zidane of the man whose two goals helped propel Madrid to a 4-1 victory over Juventus in the Champions League final in Cardiff two months ago.
That victory saw Real become the first club to retain the trophy in the Champions League era and completed a glorious campaign in which they also won La Liga.
The season started with a 3-2 extra-time triumph against Sevilla in the Super Cup in the Norwegian city of Trondheim.
"Real Madrid is a team, a club, an institution that has hunger. We all know where we are and when you finish a season like last year winning, it helps you try to do the same thing coming into the new season," Zidane -- whose team have Barcelona to come at the weekend in the Spanish Super Cup -- said in a UEFA interview.
However, his side failed to record a victory during a pre-season tour of the United States that included a high-profile friendly encounter with Jose Mourinho's United in Santa Clara, California.
That International Champions Cup encounter ended in a 1-1 draw before United won on penalties.
While the Spaniards have made two relatively low-key summer signings in Dani Ceballos from Betis and Theo Hernandez from Atletico Madrid, United have spent big ahead of their return to the Champions League.
The Europa League winners have added the defender Victor Lindelof from Benfica, the midfielder Nemanja Matic from Chelsea and Everton striker Romelu Lukaku and they wrapped up their preparations with a 2-1 win over Sampdoria in Dublin.
This match offers a chance for United to start the new campaign on a high before their opening Premier League game against West Ham United next Sunday.
In a glittering career Mourinho has not yet won the Super Cup -- his Chelsea team lost on penalties to Bayern Munich in the 2013 edition.
The Portuguese is coming up against the club he coached for three years until 2013 -- he did not leave the Spanish capital on the best of terms but he insisted that experience is not on his mind this week.
"It's something I've been through many times. I left Porto and two months later I was facing them in the Champions League," he told UEFA.com .
"I left Chelsea and a few months later I was facing them with Manchester United. I never look at it in terms of taking on my former club, not at all. So I just look at Real Madrid as what they are: a big club, the European champions, and it's a great motivation for us to play against them."
This annual meeting of the European champions and Europa League winners comes to the Balkan state after going to Prague, Cardiff, Tbilisi and Trondheim in recent years.
But in contrast to the cool conditions in Norway 12 months ago, temperatures in Skopje are expected to reach 40 degrees for much of the week.
The forecast is for it to be upwards of 30 degrees when Tuesday's match kicks off at 20:45 (1845 GMT).