Fellaini has had a new contract on the table at Everton for some time, with the impasse prompting suggestions he may move away from Goodison before the end of the month.
Cahill, though, has praised the professionalism of the Belgian, and told the Liverpool Daily Post: "The thing with players and contracts is if you want to stay you sign it and if you don't want to stay you go.
"Felli is an exceptional player and a great professional. He's put in a great performance after being out for a few weeks.
"He gives great heart to the whole team with his exceptional performances. One thing about contracts is that they always sort themselves out in the end if you really want them to."