"We will have to produce our best performance of the season to go through," was the Scot's blunt assessment yesterday.
Two goals by Dougie Freedman in the closing minutes of the first meeting at Selhurst Park on Saturday has left Wolves with a formidable task.
Yet McGhee, like his mentor Alex Ferguson, is an adept manipulator of the psychological aspects of the game and the manager will need to employ those skills fully if Wolves are to progress to Wembley and a meeting with either Ipswich or Sheffield United.
McGhee said: "The team I am able to select at the moment will have to do more than play well. They are going to have to give something extra to win this football match by two clear goals. We are really asking for what amounts to the performance of the season. If we only play well then Palace will be good enough to match us.
"There is going to have to be that extra ingredient produced if we are to make it but I don't think that's impossible to achieve."
Steve Froggatt, Don Goodman and Mark Venus, all absent at Selhurst Park through injury, will undergo fitness tests today.
In the other play-off match, George Burley may gamble on the precocious talents of Keiron Dyer at Portman Road. With Paul Mason, Ipswich's leading scorer, suffering a hamstring strain, Burley gave the England Under-19 international his first start of the season in Saturday's first-leg draw at Bramall Lane.
Now Mason is fit, but the Ipswich manager is reluctant to say whether the 18-year-old will make way. "It's a nice problem to have," said Burley, who is considering using Steve Sedgley as one of three central defenders rather than in his usual midfield role. "Keiron was outstanding and has every chance of being involved again."
In the Second Division play-offs, Brentford defend a 2-1 first leg lead against Bristol City at Griffin Park. Crewe also lead 2-1 from the first leg, but they face a difficult return against Luton at Kenilworth Road.
Hopes of an all-Wales Third Division play-off final were dented by Cardiff's 1-0 first leg home defeat by Northampton, although Swansea could still reach Wembley. They face Chester at the Vetch Field following a goalless draw at the Deva Stadium.