Celtic lacked desire, on-field leadership, depth and strength during their Champions League play-off capitulation, according to several former players.Martin O’Neill’s side squandered a four-goal aggregate lead as a 5-1 defeat by LASK in Austria consigned them to the Europa League.Stiliyan Petrov, who played under O’Neill at Celtic and Aston Villa, delivered a scathing assessment.“You have to stand up and be counted, show character, be able to deal with the pressure,” he said on Amazon Prime. “Those players were hiding.“When they had to take responsibility with the ball, they didn’t take it. They were losing the ball very easily. LASK were better in second balls, more aggressive. They wanted it more.“Celtic try to dominate games and be in control. But there was nothing there. They couldn’t take the sting out the game, they couldn’t slow the game down.“Sometimes you need big players to do that. You need players to control that, control the team. You have to stand up, be brave and be strong.“You have to run more, you have to close people down, you have to make decisions on the pitch, important decisions and important moments that make the difference. Those decisions were not there.”Former Celtic captain and manager Neil Lennon said: “Physically they weren’t up to it, running power they weren’t up to it. LASK were the better team and they wanted it more, and that’s not something you can say about a Martin O’Neill team very often.”The Dunfermline manager added: “Second half I saw three or four players go down with cramp. It’s only 65-70 minutes into the game. That’s a worry for me.“It could be a physical thing, it could be a psychological thing. For me it’s a sign of not being strong. They looked exhausted at times.”Another former Celtic captain, Scott Brown, felt the club had failed to strengthen the squad to the necessary level after bringing on Liam Scales, Anthony Ralston, Dane Murray, Luke McCowan, Reo Hatate and Sebastian Tounekti during the 120 minutes.Brown told BBC Radio Scotland: “I don’t think the subs made any impact on the game. You want something from them – running power, a bit of calmness on the ball – and we didn’t get that.“They are bringing players in that are actually in the starting 11 but it shows you, on that bench, they need better quality players to come on.”Celtic manager Martin O'Neill looks on during the Uefa Champions League game against LASK in Linz, Austria. Photograph: Christian Bruna/Getty Images Former Celtic goalkeeper Kasper Schmeichel believes the defeat will have a major impact.Schmeichel, who played in last season’s play-off defeat, said on Amazon Prime: “This is going to have huge ramifications. The Champions League is unique and the Europa League doesn’t have the same prestige. It impacts players’ lives and particularly the players that maybe we were looking to sign, that could have an impact on it.“I know it’s going to be a really, really hard reaction towards the players, towards the management.“It’s going to be a monumental task for them to motivate themselves and to get the fans back on side. Because you saw at the end, it wasn’t pleasant scenes. And we saw what happened last season, it’s not pleasant. And it’s not pleasant to be a player in that environment either.”For his part, O’Neill said the collapse from 4-0 up ranks as one of his most painful nights as the club’s manager. O’Neill has overseen more than 300 games as the club’s manager and said it was one of the most painful.“I would say absolutely, yes,” the 74-year-old said. “I’d put it down before the disappointment of losing the Uefa Cup final in 2003, but it’s so, so disappointing.“We should have been out of sight by half-time. We scored a goal, which was great, we missed two great, great opportunities. And then we give them a lifeline just before half-time and then one just after it. And they come roaring back.“And obviously we conceded, from our viewpoint, not good goals at all. But that’s my team and that’s my responsibility.”Asked whether his squad was strong enough, O’Neill said: “These are tough games. And it might only be a Champions League qualifying game, but it felt like a Champions League game. I thought they were a fine side. But that doesn’t matter. We should have been able to have seen it through. And we didn’t do. Talking about the squad, that’s for another day.”McGregor, the captain, accepted there were no excuses. “We got what we deserved,” he told Amazon Prime. “I thought we were so passive. All night. We actually looked scared to go and win the game, and when you are 3-0 up it’s psychological.“To be honest I didn’t think we were that good in the first leg either. We scored at good times and kind of got away with it. You go 3-0 and you think you’ve got a real chance but when you play like that you can’t have any excuse whatsoever.“We have to suck it up, apologise to the supporters and the club because there is no way that we should lose that game … Now you’ll see what kind of characters are in there.”