While fortified by Everton's performance in an FA Cup campaign which resulted in triumph at Wembley in May, Royle is all too aware that last season's defeat over two legs by Portsmouth was a contributory factor in toppling Mike Walker as manager at Goodison.
McCarthy's side, second in the First Division, are certain to give Royle's combative side a thorough testing. Millwall's impressive start to the campaign had been built on defensive resilience, although McCarthy feels there is room for improvement.
"We've only conceded three goals in eight games and that's because we're defending as a unit, the whole team - if I only sent the keeper and back four out tomorrow we'd certainly lose," said McCarthy, who expects to field the side which drew at Norwich on Saturday.
"I don't know whether Everton will be thinking about Portsmouth, but I know they realise what they could be in for if we win. If you're a Premiership club playing against a side from a lower division you put extra pressure on yourselves to win the game. Nobody wants to pick up the papers and read all about how they lost to a side from a lower division. "
Royle, whose side looked fragile defensively in the 3-2 defeat at the City Ground on Sunday, may recall David Unsworth in place of the pounds 2.7m summer signing, Craig Short.
Coca-Cola Cup holders Liverpool could give Jason McAteer - beaten with Bolton by Steve McManaman's double strike at Wembley last term - his first start as they begin the defence of their trophy against Sunderland. Peter Reid completed the pounds 900,000 signing of Wolves' Republic of Ireland striker David Kelly too late for him to play, with youngster John Mullin, a scorer in the win at Luton at the weekend, continuing alongside Phil Gray.
Manchester United, with their young players displaying an impressive precocity, face York at Old Trafford. Aston Villa have Tommy Johnson in for Savo Milosevic - on international duty - at home to Peterborough, while Coventry, Middlesbrough and Spurs look to make home advantage tell against Hull, Rotherham and Chester respectively.
However, West Ham's miserable start to the season - just two draws and with Julian Dicks facing a disrepute charge after the John Spencer "stamping" incident - could turn even worse if Bristol Rovers' highly rated Welsh Under-21 striker, Gareth Taylor, continues to find the net at Twerton Park.