Murdo MacLeod, the ex-Celtic player and assistant manager, has renewed hope that his former team can beat Hamburg after witnessing their performance against Kilmarnock on domestic duty at the weekend.
He was part of the BBC Radio Scotland commentary team at Celtic Park and was lavish in his praise of Tony Mowbray's side, especially in the opening period.
"They really came flying out of the traps on Saturday," said MacLeod before heading over to Germany to cover the Bhoys in Thursday evening's Europa League tie.
"I felt it was their best 45 minutes of the season. They really bounced back from the defeat in the Co-operative Insurance Cup by Hearts.
"I know they are top of the league but they have been unconvincing at times.
"Saturday's win could be the turning point in their season, when they start to convert a higher percentage of the chances they are creating."
Celtic, with just a point from their opening three encounters in the inaugural Europa League, must win to have any realistic chance of landing one of the top two places in Group C and continuing their Continental adventure.
They trail joint group leaders Hapoel Tel-Aviv and Thursday's north German opponents by five points, and old foes Rapid Vienna by three.
"A draw doesn't harm Hamburg, but it's not much use to Celtic," said the former Scotland midfielder.
"The players need to treat it as a must-win game. With the Israeli side doing so well in the group, probably unexpectedly, there are still four teams eyeing two places.
"You wouldn't put any money on Celtic getting through from the group, but if they beat Hamburg you just never know what could happen."
The Parkhead side have seen their proud European home record torn to shreds this season, with Dinamo Moscow, Arsenal and Hamburg all having left Glasgow's east end with a victory.
"Hamburg are not unbeatable, Celtic had their chances in the first leg"
But MacLeod says the players must stay positive and should look to the 2-0 win they achieved against Dinamo Moscow in the return leg of the Champions League qualifier to remind themselves that they are capable of winning on the road in Europe.
"Many of the players in the existing squad won't know too much about the club's contrasting home-and-away record over recent years," said MacLeod.
"The win in Moscow should give them belief.
"To put it simply, the good players have got to play. They just have to go over there and do the job.
"The supporters will expect them to make a go of it. They expect something from the game."
And MacLeod, who signed for Borussia Dortmund from Celtic in 1987 and made over 100 appearances for the Bundesliga side, offered the current SPL leaders hope.
"Hamburg are not unbeatable," he contends. "Celtic had their chances in the first leg, though they lost by a single goal.
MY SPORT: DEBATE"Hamburg have conceded six goals in their last two games. Borussia Monchengladbach beat them 3-2 in Hamburg on Saturday and they drew 3-3 with Schalke 04 the previous weekend.
"I would like to see Georgios Samaras and Scott McDonald both play, perhaps with Samaras playing just behind his strike partner.
"That way, Celtic will have two goalscorers on the pitch."
MacLeod would also like to see Paddy McCourt handed the chance to create openings for himself or team-mates.
He said: "Paddy will be an unknown quantity to the Germans. He's so good to watch.
"I wouldn't be unhappy if Tony Mowbray went with the same starting 11 as he played on Saturday.
"It was really pleasing to see the movement, the willingness to chase to win the ball back, the way they held the ball up and made overlapping runs.
"If they can reproduce that kind of form, they have a decent chance."
Elimination from the Champions League at the final qualifying stage by Arsenal was painful for the Glasgow side.
Defeat in Germany on Thursday would make a subsequent exit from the Europa League a virtual certainty.
Celtic's task is clear.
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