Ronaldo is suspended for his country's World Cup qualifier against Azerbaijan next Tuesday following his booking against the Republic of Ireland on Wednesday night.
The 36-year-old took off his shirt after scoring a stoppage-time winner in Portugal's 2-1 victory, having also scored their 89th-minute equaliser.
Fernandes Santos, Portugal's head coach, has allowed Ronaldo to leave the camp despite his captain being eligible to play in Saturday's friendly against Qatar.
A statement by the Portugese Football Federation read: "Cristiano Ronaldo was discharged from the national team stage this Thursday.
"The yellow card against Ireland, as the second in this qualifying round, requires him to serve an official penalty match, which will follow against Azerbaijan.
"This morning, the captain of the national team was part of the group of players who performed recovery work at the hotel.
"Fernando Santos also led a training session on a lawn next to the hotel unit used by the national team during his stay in the Algarve."
The first of Ronaldo's goals against Ireland saw him become the all-time leading goalscorer in men's international football, moving clear of Iran's Ali Daei.
The United forward, who has now scored 111 goals for his country, is set to make his second debut for the club against Newcastle United on 11 September.
Ronaldo completed a £19.8m move to United from Juventus earlier this week, having left Old Trafford for Real Madrid in 2009 for a then-world record fee of £80m.
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