The Spain international is thought to be high up on Louis van Gaal’s transfer wish-list this summer as the United boss looks to bolster his defensive options at Old Trafford ahead of his second season in charge at the club.
However, Carvajal concedes that he would find it difficult to see Ramos playing for a team other than Real Madrid next season.
Asked if Ramos could be on his way to Manchester United this summer, Carvajal told AS: “I don’t know.
“All I do know is that he is a team-mate of ours and a cornerstone of Real Madrid, and no one can imagine him in the shirt of another club.”
Ramos has won three La Liga titles, three Copa del Rey crowns and the Champions League.
The Real Madrid defender is set to become a free agent in the summer of 2017 unless the World Cup winner agrees a new deal with the 10-time European champions.
The World Cup winner scored four goals in 42 games in all competitions for Los Blancos last term.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news