The Blancos captain said he would give Busquets "a slap" after the Catalans defensive midfielder was pictured planting his boot on Pepe's head in March's Clasico, which Barca won 4-3.
Xavi responded by saying that "Busquets never stomped on Pepe, you can see in all the images that there’s nothing to it" and criticized Madrid's Spain contingent for being "very unfair" to their international teammate.
This served to irritate Casillas further, however, and he has denounced his colleague's comments, urging Xavi to stop airing his issues in public.
"If Xavi has a problem with me, he has to talk about it calmly to me and not give out free publicity to fill TV shows," he sniped after Real Madrid qualified for the Champions League semifinals despite losing 2-0 at Borussia Dortmund on Tuesday.
"We don’t need to give it any more thought. Let’s put it to one side, as it’s boring and tiresome."
Real Madrid faces Barcelona once again on April 16 in the Copa del Rey final.