As things stand going into the second half of qualifying, it looks like only one of the Republic of Ireland or Scotland will be able to qualify for the Euro 2016 finals from Group D.
The two sides go into Saturday's match separated by just two points in the table behind surprise pacesetters Poland and world champions Germany.
Ireland
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It has all been pretty rosy for the four home nations in qualifying, but Ireland are in real danger of dropping off the pace in Group D if they suffer defeat in two days' time.
A Scotland win is likely to put the Boys in Green five points behind the top three as Poland host Georgia and Germany travel to minnows Gibraltar. Missing out on qualification would be all the crueller if the four nearby UK nations make it - England, Wales and Northern Ireland are all going strong in their respective groups.
Failing to win would also make it just one victory in six for Martin O'Neill's side, who played out a dire 0-0 draw with England in their warm-up friendly on Sunday.
Ireland had a pleasant start to qualifying and began with two wins out of two against Georgia and Gibraltar. Next was a trip to the world champions and their campaign was given a huge boost when John O'Shea came up with a 94th-minute equaliser in Gelsenkirchen.
Since then, however, they went down 1-0 in the reverse to Scotland and needed another late equaliser from Shane Long to share the spoils with group leaders Poland.
Their only win in their last five matches was a 4-1 friendly victory over the United States - a result that looks all the more impressive now given that the US have beaten both the Netherlands and Germany in the past week.
Preparation hasn't been perfect, with O'Neill and his assistant Roy Keane involved in a minor car crash. Neither man was hurt.
Recent Euro 2016 qualifying form: WWDLD
Recent form (all competitions): WDLWDD
Scotland
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While Ireland had an easy start to their campaign, Scotland's couldn't have been more difficult with a trip to Germany. They couldn't match Ireland's feat of getting anything from the world champions, but put in a valiant performance and only lost 2-1 in Dortmund.
Since that early setback, they have dropped only two points in four games and that came in an impressive 2-2 draw away in Poland.
In all competitions Gordon Strachan's side have lost just once - a 3-1 defeat at home to neighbours England - in their last seven matches, with their last five all at home.
The Scots haven't competed at a major tournament since the late '90s when they made early exits at both the Euro 1996 in England and the 1998 World Cup in France.
In the latest FIFA rankings, Scotland climbed two places to 28th, which is 32 places above opponents Ireland in 60th.
Recent form: LWDWW
Recent form (all competitions): DWLWWW
Team News
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The big question for Ireland is whether all-time top scorer Robbie Keane will be deemed fit enough to start in this big game.
The veteran forward has played little football since April because of a groin injury, but did start for the Los Angeles Galaxy on Saturday.
If Keane doesn't start, O'Neill could again start with Ipswich Town duo Daryl Murphy and David McGoldrick, who led the line for the Irish against England.
It will also be a big decision for O'Neill if he starts Aiden McGeady, who is loathed by some Scottish supporters for opting to play for Ireland despite being born and raised in Scotland.
For the visitors, Strachan must decide whether to start Bournemouth's Matt Ritchie or not. The winger was Bournemouth's standout player as they won the Championship for Premier League promotion last season and scored his first international goal in Scotland's warm-up friendly against Qatar.
There is also a conundrum for Strachan in defence, with Russell Martin set to start but the other centre-back spot up for grabs. Grant Hanley would usually accompany the Norwich City man, but he is injured and Strachan must now decide between Charlie Mulgrew, Gordon Greer and Christophe Berra to slot in.
Ireland possible starting lineup:
Given; Coleman, O'Shea, Wilson, Brady; Hendrick, McCarthy, Whelan; McGeady, Murphy, Long
Scotland possible starting lineup:
Marshall; Anya, Greer, Mulgrew, Forsyth; Brown, McArthur; Ritchie, Maloney, Anya; Naismith
Head To Head
Shaun Maloney's goal from a cleverly-worked corner 15 minutes from time proved the difference in the November reverse as Scotland came out on top at Celtic Park.
That was the two sides' first meeting since the Nations Cups of 2011 when Keane scored the only goal in their last encounter at the Aviva Stadium.
Before the two most recent meetings, the home side hadn't won a match between these two since 1961.
We say: Ireland 1-1 Scotland
A draw suits the Scots better and Ireland have been struggling in front of goal recently with just two goals in their last three qualifiers. Granted, those games have come against the three sides above them in the table, but O'Neill's men will have plenty of pressure on their shoulders and might not be able to break the Scots down all that often.
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Spain
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