A controversial offside decision means Swansea's quest to secure a place in the knockout stages of the Europa League will go to the wire after their 1-0 defeat to Valencia at the Liberty Stadium.
A draw would have been enough to take the Swans through from Group A with a game to spare, but they fell behind to Daniel Parejo's 20th-minute strike and then lost striker Wilfried Bony to a hamstring injury.
They thought Alvaro Vazquez had levelled just before the break when Diego Alves could not hold Jonjo Shelvey's shot and the Spaniard tapped in -- but the flag went up. Replays suggested the two Swansea players had been onside.
If the goal had stood, it would have been enough to seal a spot in the last 32, but Swansea must now wait until their final game against St Gallen to find out their fate.
Michael Laudrup's side are three points clear of third-placed Kuban Krasnodar, with the Russians having to go to group winners Los Che in the final round and Swansea three goals better off.
Valencia were much improved from the first meeting between these two sides and deserved their lead. Gerhard Tremmel did not deal with a Sergio Canales corner, and Parejo slotted home when Juan Bernat's deflected shot fell to him.
Parejo went close to a second and forced Tremmel into sprawling save before Swansea saw Bony pull up as he chased a long ball.
The key moment soon arrived as Bony's replacement Vazquez finished from close range only to see his effort chalked off.
And the Welsh club's night was summed up when Jeremy Mathieu cleared a goalbound effort off the line and Angel Rangel limped off in the dying minutes.
Swansea had won when the sides met at the Mestalla in the opening round of Group A fixtures, but there appeared little chance of a repeat as Valencia started with an authority and crispness in their passing.
However, it was the hosts who had the first real chance. Alves punched an Alejandro Pozuelo corner straight at Bony, who headed it just wide of the left-hand post.
Nathan Dyer also threatened in the air from a Neil Taylor cross before the Welsh club fell behind. They responded with an extended spell of pressure but failed to work Alves, with Tremmel the busier keeper.
The German had to tip a low Parejo shot away as it headed for the bottom corner, while Jonas worried him with a fizzing drive from distance.
Swansea sepped up the pace and pressed for the goal that would have put them through as substitute Jonathan de Guzman forced a save from Alves, who also kept out Vazquez's follow-up and a misdirected Pozuelo effort.
Vazquez was then denied again as Mathieu superbly blocked on the line after the striker had beaten Alves.