The pair were rumoured to have quarreled after the award ceremony for the Uefa Best Player in Europe, but those allegations now appear to be wide of the mark
The picture was uploaded following the Blancos' 2-0 Liga victory at Rayo Vallecano, in which both the goalkeeper and winger starred, and bears the caption: "You'll have to take this with humour".
The champions have made a disappointing start to their title defence, coinciding with Ronaldo's claims that he was unhappy at the Santiago Bernabeu in the aftermath of a league match against Granada.
An article in El Confidencial Digital also referred to a dressing-room incident between the pair, which had arisen from the inauguration of the Uefa award for Best Player in Europe.
Rumours had suggested that some of the Spanish players in the Madrid squad were happy and even laughed when Andres Iniesta pipped Ronaldo to the individual honour.
Their relationship was further called into question after Casillas appeared not to celebrate the forward's last-gasp winner in Madrid's 3-2 Champions League triumph over Manchester City.