For Celtic to progress to the last 16 of the Europa League, they are going to have win a competitive match in Spain for the first time.
Last week's 2-0 first-leg home defeat by Valencia means Brendan Rodgers' side must score at least twice without reply at the Mestalla to stand a chance of staying in the competition.
Here, BBC Scotland looks back at some of their trips to Spain.
Celtic have faced Barcelona more than any other Spanish side - 14 meetings in total. Most of those have ended in Barca wins, both at the Nou Camp and Celtic Park.
However, Celtic claimed two significant draws away to the Catalan giants in 2004.
In the second half of the 2003-04 season, Celtic were bidding to reach a second successive Uefa Cup final and found themselves paired with one of the tournament favourites.
Alan Thompson's goal gave Martin O'Neill's men a narrow win in Glasgow and goalkeeper David Marshall's heroics ensured a 0-0 draw in Barcelona to secure a 1-0 aggregate victory.
Celtic were knocked out by Barca's La Liga rivals Villarreal in the next round, but the following season O'Neill's side were back in Europe in the Champions League.
Henrik Larsson, having just left Celtic, scored in a 3-1 win for Barcelona in the group opener but the Swede missed the return match when John Hartson cancelled out a Samuel Eto'o opener to seal Celtic's first ever away point in the competition.
John Hartson's goal earned Celtic a draw in Barcelona in 2004
Maurice Johnston was on target as Celtic claimed a respectable 1-1 draw against Atletico Madrid in a European Cup Winners' Cup tie in 1985.
But Celtic lost the home leg to go out 3-2 on aggregate.
The Glasgow giants returned to Metropolitano Stadium in 2011, but lost 2-0 in the Europa League.
Celtic's previous two visits to the Mestalla have ended in defeat.
The first was a 4-2 first-leg defeat in the old Fairs Cup in 1962, the second leg ending 2-2.
And, in 2001, Martin O'Neill's Celtic, having dropped out of the Champions League and into the Uefa Cup third round, lost 1-0 in Valencia and went out on penalties.
The Scottish champions have also lost away to Real Madrid, Real Sociedad and Celta Vigo, though the away goal scored against Celta was enough to send them through en route to the 2003 Uefa Cup final.