CELTIC could have had a double by now yet suddenly they're being handed criticism rather than trophies.

Since October they have cruised past all domestic opponents only to suddenly and surprisingly stall in front of the finishing line. Even five months of relentless winning offers only a gossamer-thin protection against questions being asked of an Old Firm club and Celtic have found themselves being dissected. Worse still, an old and wounding accusation has risen up against them.

Last year they lost the League Cup final to Rangers and went down in a shocking performance in Inverness just when the league title was in their hands. Now they are stuttering again at the business end of another campaign. Do these generally impressive, consistent players have a problem holding their nerve? Even some derby successes and victory in the Scottish Cup final have not entirely addressed a sense that Celtic still have a persistent flaw. There are days, big days, when four or five key men go missing.

What they have shown beyond doubt this season is that they are the best team in the country, a team which would have been champions even if Rangers had not been stripped of 10 points for going into administration, but recent matches have seen the resurrection of old accusations. Celtic had by far the most chances in the Scottish Communities League Cup final against Kilmarnock but they fluffed them and defended horribly to lose the game's only goal. They claim that Cha Du-Ri's red card was the game-changer in Sunday's Old Firm defeat, yet responded far more impressively when Fraser Forster was sent off in the first half of an Ibrox derby 13 months ago, when they came from behind to draw in the William Hill Scottish Cup.

Losing to Kilmarnock in the cup final was most obviously attributable to poor finishing and poor defending, and against Rangers they were unable to carve their name into club history by clinching a championship at Ibrox because of indiscipline and, again, an unconvincing contribution from the men at the back.

Inevitably, though, Celtic must fend off questions about their temperament on the back of two significant consecutive defeats. It is raw and painful for professional footballers to have their strength of character questioned. Still, in Scottish football parlance, do Celtic lack bottle?

"I think that's nonsense, to be honest," said Thomas Rogne, the Celtic defender yesterday. "We've played a lot of big games and we've lost two big games now, but that happens. I think the game we played against Rangers on the 28th of December [Celtic won 1-0] was an even bigger one because they were close to us on points then. We won the cup final last year – that was a big game – but if we lose two now people start to talk about our mentality being bad. That's nonsense.

"We have strong characters in our dressing room. That's one of the things the manager wanted to change when he came in. The group was a bit down but he changed our mentality and he changed our character. We were 15 points behind and somehow we managed to be 18 points in front, so something's happened there and I don't think you have a weak mentality if you manage to do that.

"We don't care what other people say about us or expect of us from the outside. If we win the league I think that's all that matters, really. At the end of the season that's all you think about: did you win the league or not?"

They will have it won soon enough and any criticism and doubts will melt away for a while, but in the meantime there are clouds because of the consecutive defeats and the new swirl of disciplinary issues around Neil Lennon. The manager was sent from the technical area at half-time after a confrontation with referee Calum Murray. That incident came only days after the Scottish Football Association asked Lennon to explain his outspoken criticism of another official, Willie Collum, at the cup final. Both episodes are the subject of disciplinary action which could lead to Lennon being suspended from the technical area just as his team nears the result it needs to confirm the championship.

Oddly Rogne had not noticed Lennon was missing from the dugout until midway through the second half, such was the noise at Ibrox, yet the Norwegian still regards his manager as an enormous presence in every match. "We want him the way he is," he said. "That's how he got us here and we don't want him to change at all. In these [Old Firm] games you don't really hear instructions from the dugout because it's so loud. But of course we want him on the bench because that's where he belongs.

"If he has to be in the stands [because of a suspension] then we will have to deal with that and I think we would. All the players will always be behind the manager."

n Rogne was speaking in Glasgow to promote ESPN's coverage of forthcoming SPL games including Motherwell v Rangers on March 31, Caledonian Thistle v Hibernian on April 1, Kilmarnock v Celtic on April 7, and Hibernian v Motherwell on April 8.