Celtic could be heading out of the Europa League after suffering a 1-0 defeat at home to Atletico Madrid.
The Spanish outfit, who are considered one of the favourites for the tournament, secured qualification with the result.
Arda Turan, a summer arrival from Udinese, scored the only goal of the game on the half-hour mark.
The Turkish midfielder powered a 20-yard shot past Frazer Forster in the Celtic net after Daniel Majstorovic had cleared Diego's corner.
The Bhoys' first half was made worse when Wales midfielder Joe Ledley was stretchered off and replaced by Charlie Mulgrew.
Neil Lennon's side rarely threatened an equaliser while the visitors looked a constant threat going forward.
Gary Hooper was introduced at the break but Celtic could not get back into the game.
The Scottish outfit now need to beat Udinese in Italy in order to progress.
