Needing to score at least twice in order to overturn the 2-1 deficit, the odds are certainly stacked against Diego Simeone's side.
Nowhere is that sentiment more evident than the quote of just 1/20 (1.05) that the Catalan giants qualify for their fourth consecutive Copa Del Rey final.
That price is unlikely to tempt many punters into a wager but Betfair have a new customer offer of 3/1 (4.0) available for anyone opening an online account.
Simply register using the links provided, back Barca to qualify at the usual odds and if they do, the returns will be topped up to a massive 3/1 (4.0) by the online firm. Winnings are paid in free bets. T&C's apply.
As if the task wasn't tough enough for an Atleti side who are around 4/1 (5.0) to record what looks an unlikely victory, Luis Enrique was able to rest some of his stars in the weekend win over Athletic Bilbao.
Luis Suarez sat out that game and La Liga's two leading scorers look set to be reunited as the Uruguay international joins Lionel Messi and Neymar in the potent front three. The visitors have plenty of firepower too of course, but Barca's impressive recent run means Simeone's men face a real uphill battle if they're to reach the showpiece finale.
The home side are just 4/7 (1.57) to win the game, but backers of the 3/1 (4.0) don't even need Barcelona to do that in order to land their bet. A draw would be enough to see the overwhelming favourites through of course, as would a 1-0 defeat due to the first leg result.
The 3/1 (4.0) on offer is a huge price enhancement and is expected to prove extremely popular with anyone yet to register with Betfair.