Edinson Cavani said he feels 'sad and upset' for missing the upcoming three rounds of World Cup qualifiers with Uruguay.
Cavani has agreed to swap to 21 -- the number the veteran striker wears for Uruguay -- so Ronaldo can reclaim his old jersey.
Edinson Cavani scored from the penalty spot in the 21st minute for the only goal of the match at the Nilton Santos Stadium in Rio de Janeiro on Monday.
Paraguay went second in group A behind Argentina with a 2-0 win over Chile, who dropped to third with Uruguay fourth.
Last month, Cavani ended uncertainty over his immediate future by committing to a second season with the Red Devils, to the delight of United's fans as well as his manager Ole Gunnar Solskjaer.
Cavani has been a huge hit at Old Trafford since arriving as a free agent in October, both with his goals and assists but also with his attitude and application.
City still needs three points from its final three games to seal a third league championship in four years under Pep Guardiola, and a fifth in 10 seasons in total.
France became the first team to reach the World Cup semi-finals on Friday after an assured 2-0 win against Uruguay.
The Paris Saint-Germain striker scored both his side's goals in the 2-1 victory in Sochi in their last-16 tie, before hobbling off with a calf problem.
Edinson Cavani fires Uruguay into last eight as Portugal striker Cristiano Ronaldo's World Cup dream ends
Cavani curled home a superb 62nd-minute winner to settle a thrilling second round duel in Sochi which sends Uruguay into a quarter-final against France next Friday.
Uruguay head into their first game against Egypt with the focus on stars such as Luiz Suarez but with their World Cup hopes equally resting with veteran coach Oscar Tabarez.
The Celeste have been widely tipped to top a relatively weak-looking group, which contains hosts Russia, Saudi Arabia and Egypt.
After the striker was expelled from the 2014 tournament in disgrace for biting Italy defender Giorgio Chiellini, Uruguay was eliminated by Colombia in the round of 16.
The Celeste, welcomed by a small group of fans at the city's airport, will be based in Bor, some 20 kilometres from central Nizhny.
Edinson Cavani and Luis Suarez were born in this northern Uruguayan river town just three weeks apart in the late austral summer of 1987.