The Cottagers' £11 million summer signing was the subject of ridicule from supporters of his former club.
The former Leeds United striker was unable to influence matters on the field during his side's 2-1 defeat to Ipswich Town and was duly taken off by his coach in the second half.
"He has to improve his fitness and I don't know how long that will take," Magath told reporters after the game.
"Ross came to us with a lack of fitness and not at the beginning of pre-season. He is not at the same level as the rest of the players.
"I wanted him to be fit when we signed him but at the moment he is not in the right shape. When he does, he will be the perfect striker for us."
But McCormack's misfortune at least presented one set of fans with a glimmer of hope - those of his old club.
Earlier on Saturday afternoon, Leeds had lost their Championship opener at the hands of Ian Holloway's Millwall side.
The knowledge that their former forward was having a similarly bland day, then, was a source of comfort to some of their supporters - and the opportunity to poke fun at the 27-year-old's debut proved too good to miss for some.
Ross McCormack after being subbed: "This is not the Fulham I fell in love with!"— Liam Tulley (@liamtulley) August 9, 2014
McCormack puts in a transfer request after Fulham are just as ambitious as Leeds.....— Alex Narramore (@AlexNarramore10) August 9, 2014
Be careful #fulham, 56 minutes of first team football means McCormack will be asking for a Pay rise.— Daniel Brader (@Castrobrader) August 9, 2014
Impressive debut for McCormack at Fulham eh?— Jon Maclean (@JayMacLUFC) August 9, 2014