There are 4 Spanish teams in the knockout stages and you cannot be paired with a team of your country in the Round of 16. They cannot face Atletico and Barca, who finished first of their group. They can also not face Dortmund, who were in the same group. Therefore, they can only face Leicester, City, Monaco, Arsenal, and Juventus.
We can get anyone who finished second except Sevilla, so we have the best chance to get Madrid because they can only play against 4 teams.