Ronaldo was suspended for one game Tuesday and will likely miss Real Madrid's match against FC Barcelona this weekend.
The Spanish soccer federation rejected Madrid's appeal against the yellow card Ronaldo received for an 82nd-minute foul during his team's 1-0 defeat at Getafe on Saturday.
The Brazilian striker was sent off eight minutes later, following his second caution for making a remark to the referee.
Ronaldo's ejection was his first in the Spanish league.
The federation's decision appears to have denied Ronaldo the chance to face his former club in Sunday's game at Santiago Bernabeu Stadium. The 30-year-old spent the 1996-97 season with Barcelona, scoring 34 league goals.
However, Madrid has the option of going to the federation's appeals committee in a bid to have Ronaldo's suspension rescinded.
Madrid lies fifth in the league with 11 points, five behind leader and defending champion Barcelona.
© The Canadian Press, 2007