Spanish boss Vicente del Bosque's line-up for the opening game against Italy caused some consternation when he named a team without a single specialist striker in it.
However, the Euro 2008 and 2010 FIFA World Cup™ champions emerged with a point from arguably their toughest group match, and will now turn their attention to booking a place in the last eight by ending Ireland's hopes of joining them.
Manager Giovanni Trapattoni has admitted he does not know what to expect from Del Bosque, but Keane is confident he and his team-mates will be prepared for all eventualities.
He said: "We will prepare for if there are six midfielders and if there are strikers also. The manager will have videos on both situations and I am sure we will be well aware of how to play against them.
"We know no matter who they play, it will be a tough ask because the players they have are world-class players, and they have probably six of the best midfielders in the world.
"Listen, it's going to be tough, but we have to believe we can go into the game and get three points, and in the worst case scenario, we get a point."
Full-back John O'Shea and his defensive colleagues will perhaps be most affected by the way Spain set up, but he knows they will face the sternest of examinations regardless of personnel or system.
O'Shea said: "Look, that's Spain's decision. We will be preparing for both eventualities because no matter if they play with a striker or not - they could turn up with two strikers against us, so we will see.
"But whoever they play, they are going to be good players, so we are going to have a good test."
Last throw of the dice
Trapattoni too has decisions to make in the wake of Sunday night's 3-1 defeat by Croatia in Poznan.
His normal approach simply did not pay off in that game as uncharacteristic defensive errors ripped his best-laid plans apart, and there have been calls for him to attack Spain rather than sit back and risk more of the same.
However, O'Shea is happy to leave those decisions to the 73-year-old. He said: "That's why we have the manager. All the fans can't be the manager.
"The manager has got us to the tournament and he gets the choice to make those decisions. We have to have our trust in him - and we do - and we will back him to the end."
Trapattoni has hinted that striker Jon Walters might get the nod for the Spain game, but whatever team he picks, O'Shea knows the painful memories of what happened against Croatia must be forgotten.
He said: "When you go into a game like that at the start of a tournament, you want a positive start.
"But we didn't get it and we can't dwell on it now. We have to move on to Spain, and it's one we are looking forward to."