The Republic of Ireland are already without Quinn's normal partner, Robbie Keane of Coventry, and ruling out the Sunderland man, who aggravated a neck injury while warming up before the 1-1 draw in Dublin on Saturday, would impair their chances of achieving the victory or high-scoring draw required to reach the finals for only the second time.
It could also force a change of tactics as well as personnel. David Connolly, the little forward banished by the Dutch club Feyenoord to their nursery side Excelsior, has already been told he is Keane's replacement, but McCarthy will be understandably reluctant to give another start to the 37-year-old Tony Cascarino, whose inadequacies were underlined again in the first match.
"We are going to leave it until the morning and see if there is any reaction," McCarthy said. He would be strongly tempted in Quinn's absence to support Connolly with two attacking flank players and bolster the midfield by putting Lee Carsley or Alan McLoughlin alongside Roy Keane and Mark Kinsella, whose return after suspension is one of the more positive aspects of the squad's preparation for Ireland's most significant match since losing a World Cup play-off to Belgium in similar circumstances two years ago. Stephen Carr, Kenny Cunningham and Gary Breen should all be fit.
The competition has proved to be a long and tortuous road for the Irish. As they enter the final section of this particular stage, McCarthy is inclined to believe that good and bad fortune probably levels itself out even though they were so close to qualifying before late goals denied them in Croatia and Macedonia.
"We've had a bit of luck as well" McCarthy said. "What if Croatia had scored in the last minute against Yugoslavia, or if Alan Kelly hadn't made that save in Malta? We'd have been out. I don't believe I'm unlucky. In my life and my career I've been very fortunate. But if there's any going, I'd like to take a piece."
Attempting to make some luck by going at the Turks would be an interesting approach, partly because the hosts will hardly expect it and partly because an Irish goal could expose one of the Turkish nation's perceived weaknesses, shown in Galatasaray's collapse against Chelsea recently once things began to go against them. There would, of course, be a risk of conceding on the break, but whether level at 1-1 on aggregate or 2-1 down, Ireland would still need to score.
A key figure could be Kevin Kilbane, West Bromwich Albion's former Preston winger, whose Lancastrian accent betrays his birthplace but obscures his family's Irish history. So devoted does he feel to the green cause that as a teenager he refused to attend an England youth squad get-together, reluctantly travelling later although "my heart wasn't in it".
Like most of the younger Ireland players, he grew up watching Jack Charlton's teams reach the 1988 European Championship finals - where they famously defeated England - and then in the World Cups of 1990 and 1994.
A frustrated substitute for the defeat in Belgium, he performed well when given a chance on Saturday by Mark Kennedy's injury. He might have scored twice and the performance has further boosted his levels of confidence that have slowly improved since a disappointing international debut in Iceland two years ago. Now he should not be deterred by the prospect of a crowd whose hostility is likely to make a West Bromwich against Wolves fixture look and sound like a stroll in the park.
Turkey's record of having beaten Ireland only once in ten attempts is now something of an irrelevance given their startling strides up the Fifa rankings of late.
The Fenerbahce midfielders, Sergen Yalcin and Abdullah Ercan, and the Galatasaray strikers, Hakan Sukur and Arif Erdem, illustrated in Dublin what good players they are and Ireland will need Kinsella and Roy Keane to disrupt the flow from the middle and to set up plentiful supply of their own if the luck of McCarthy's adopted country is finally to hold good.
REPUBLIC OF IRELAND (v Turkey, European Championship play-off second leg, Ataturk Stadium, Bursa, 6.0): (from) Kiely (Charlton); Carr (Tottenham), Breen (Coventry), Cunningham (Wimbledon), Irwin (Man Utd); McAteer, Duff, Carsley (all Blackburn), McLoughlin (Portsmouth), Kinsella (Charlton), Roy Keane (Man Utd), Kilbane (West Bromwich Albion); Connolly (Feyenoord), Quinn (Sunderland), Cascarino (Nancy).