Everton crashed out of the FA Cup to Reading on Tuesday
Fellaini picked up his knock during Everton's 2-0 Premier League win on Saturday against Sunderland. The Belgian caught his foot in the ground as he attempted a challenge, however, it is believed that the former Standard Liege man aggravated an old problem and will undergo surgery on his ankle next Monday, which rules him out for the remainder of the campaign.
Australian international Cahill came on for the last 15 minutes of the 2-0 win at the weekend but it appears he will miss Everton's trip to Newcastle United on Saturday, as well as the home matches against Birmingham and Fulham on the 9th and 19th of March respectively.
Everton's misery worsened on Tuesday following their 1-0 defeat to Reading, which dumped them out of the FA Cup and Moyes insists injuries to the two midfielder's should not have influenced the result.
"Marouane Fellaini is going to be out for the season now, he'll have an operation on Monday," Moyes told reporters.
"Most people will tell you he's been a key key player for us this season.
"Tim Cahill will miss two or three weeks with a foot injury just now, but that isn't a reason for tonight's result [Everton's FA Cup exit to Reading]."