Celtic held by ten-man AEK Athens in qualifier first leg
The Hoops must score in Greece if they are to progress in Champions League qualifying.
Celtic were held to a 1-1 draw as ten-man AEK Athens grabbed the advantage in the Champions League third-round qualifier.
Callum McGregor put Brendan Rodgers' side into the lead at Celtic Park with a neat finish, but the Greek champions responded through Viktor Klonaridis before the interval.
Athens midfielder Konstantinos Galanopoulos was sent off with over half-an-hour left but Celtic were unable to find a winner on their own patch and now must score at least once in Greece.
The Hoops had started brightly, with marauding full-back Keiran Tierney a constant threat down the left.
The 21-year-old twice threatened to set up the opener in the early stages but his deliveries were cut out at the last moment.
It would be third time lucky for Tierney, though, as the Scotland defender found his international colleague McGregor with a cut-back and the onrushing midfielder finished clinically.
Playing their first competitive match of the campaign, Athens took their time to grow into the fixture.
While Celtic left-back Tierney was a huge influence from the start, his opposite number Helder Lopes became prominent as the half wore on.
First, the Portuguese wing-back tested Craig Gordon from range, forcing the Scotland stopper to tip his dipping effort over the bar.
Lopes then set up the visitors' equaliser by digging out a cross from the byline for Klonaridis to control and slam the ball into the net.
Just before the hour mark Athens were reduced to ten men. Galanopoulos, who had been booked for a foul on Tom Rogic five minutes earlier, received a second yellow for tripping James Forrest as the winger sped away.
The Greek champions dropped deeper thereafter as Celtic probed to restore their lead.
Substitute Leigh Griffiths headed over Forrest's tempting cross before Scott Sinclair spurned an opportunity to make an immediate impact off the bench.
Rodgers' side struggled to break through as the match wore on. Midfielder Olivier Ntcham went close in the dying moments but the Greek champions saw out the match to take the advantage in the qualifier.