Martin O'Neill admits three straight defeats "doesn't augur brilliantly" for Celtic's chances of progressing in the Europa League but believes his side are still capable of qualifying as they prepare to host Besiktas on Thursday.

The Scottish champions and current Premiership leaders suffered another blow on Sunday with a 2-0 defeat away to Falkirk that means they have won just three games in their latest 10 games overall.

Manager O'Neill also admits that he does not yet know his best starting XI following a summer of squad changes and injuries.

"No, I keep getting asked this question and until I know exactly what everyone can do at the football club then I probably won't know that," O'Neill said.

O'Neill pointed out that having such clarity is made more difficult because "we're rotating a bit as well to try and save some legs" during a heavy schedule of games while some new signings and some recovering from injury had not yet "had a proper opportunity".

"For Celtic, generally it can be a trying time, but we have to get through it," O'Neill said.

"I've experienced these in the past and it's a matter of, I think, maybe giving the players confidence again to go and play their very best under difficult circumstances."

O'Neill pointed out that LASK and Benfica - two sides who have humbled Celtic so far this season in Europe - had since proved their respective qualities.

Asked if he agreed with centre-half Liam Scales that it is not a must-win game against Besiktas, the manager said: "We need to get off the mark at some stage.

"I was told that, statistically speaking, any team who's lost their first three games haven't made it through, so it doesn't augur brilliantly for us if that's the case.

"So if we go on for a fourth one then that would be a world record. We're definitely running out of matches, no question about it, but we are capable of still qualifying."

Besiktas, in contrast, sit eighth in the Europa League table after two wins and a draw.

O'Neill reckons the Turkish side will be disappointed to be only sitting fourth in their domestic league but predicts they will be "a real handful", pointing out that striker Oh Hyeon-gyu might have "a point to prove" after an unsuccessful time with Celtic.

The South Korea striker, who scored 12 times in 18 months with Celtic but only started six times, later confirmed just that.

"I'm so excited - it's very special for me to be back here," the 25-year-old said. "It was sometimes hard for me, but Celtic became like my second home.

"Finally I am back here and I have to show them. Maybe I will be emotional if I score."

Besiktas head coach Vincenzo Italiano faced Martin O'Neill's Celtic in the Europa League earlier this year in a 2-2 draw in Bologna.

"I'm very much surprised they have zero points, so we might see a very angry Celtic," he said. "This might complicate our job."

Thursday's game comes just too soon for Celtic winger Yang Hyun-jun, who is back in training after injury but is more likely to return to domestic action on Sunday.

Former Chelsea youth centre-back Umit Akdag misses out for Besiktas through suspension after his straight red card for a dangerous tackle on Jorgen Strand Larsen with 13 minutes left of their 2-2 draw with Crystal Palace.

Only two midfielders - former Brighton and Arsenal playmaker Leandro Trossard and ex-Leicester City man Wilfred Ndidi - and goalkeeper Alexander Nubel kept their places for the 2-0 win over Basaksehir in the Turkish Super Lig.

Head coach Vincenzo Italiano then named an unchanged team for Sunday's 2-2 draw with Kasimpasa in which former Rangers left-back Ridvan Yilmaz set up Trossard's opener and ex-Ibrox winger Vaclav Cerny was taken off early for the second game in a row.

Former Wolverhampton Wanderers centre-back Emmanuel Agbadou and on-loan Aston Villa defender Yasin Ozcan also started both domestic games.

Oh came off the bench in both games having started Besiktas' previous two in the Europa League, scoring twice and also contributing an assist in his three games in the competition this season.