The Kansas City Royals recognize that they need an ace if they're going to win the World Series.

They nearly acquired one Saturday.

The Royals were close to trading for Cincinnati Reds ace Johnny Cueto before the deal fell through, major-league sources told FOX Sports.

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The issue, the sources said, was that one of the players going from the Royals to the Reds did not check out medically. At that point, the deal was nullified.

The near-trade created a dramatic scene among Reds officials and players prior to their game Saturday evening against the Colorado Rockies. Not long before the first pitch, Cueto's fellow starter Michael Lorenzen began warming up because the Reds believed there was a high probability Cueto would be scratched once the deal was formally agreed upon.

Instead, Cueto started the game as scheduled -- and performed brilliantly, earning the victory with eight shutout innings. There remains a strong probability that Cueto, a free agent after this season, will be dealt by Friday's 4 p.m. ET non-waiver trade deadline.