Gerry Armstrong has not been on the phone to Neil Lennon this past week.
But the former Northern Ireland internationalist and La Liga TV pundit will be the first to congratulate his fellow countryman should Celtic pull off a surprise in the Nou Camp tonight – something that he believes the Parkhead side are capable of doing.
Yet, as Lennon took in Barca's 5-4 win over Deportivo de la Coruna on Saturday evening, he would not have needed to chat to anyone to realise just how potent a threat the Catalans are. Nor would he need to be reminded of just how good Lionel Messi is.
The Argentine underlined his status as arguably the best player in the world with a hat-trick, goals that take his tally to 71 in this calendar year. It is worth noting that the previous best in a year was Pele in 1959 with 75.
Barcelona underestimating Celtic is perhaps a small glint of light that the Parkhead side can hope for.
But, while the current Barcelona side are currently regarded as one of the greatest ever club teams, Armstrong has told Celtic that they do have weaknesses, and they can be exploited.
"Defensively Barcelona get away with a lot because they are always so good at scoring at the other end," he said. "But if you are going to get at them, then set-pieces are the way to do it.
"In contrast to Celtic, they are a very small team.
"They have only three outfield players who are over 6 foot – Gerard Pique, Alex Song and Sergio Busquets – and if Celtic can grab themselves a free-kick in a decent area, or a corner, then they need to look to try and make that count.
"Without doubt it will be the best way for them to sneak something.
"I watched Celtic's game in Moscow, in their last Champions League game, and it is the same kind of togetherness and application that they will need tonight.
"I know Neil, I've not had a chance to speak to him yet but I think he'll know what kind of standard is required tonight. It is a difficult, difficult task to compete against a side like Barcelona who are full of top internationalists.
"But if they are vulnerable anywhere, it is at the back."
Whilst a useful tip, this, of course, will rely on Celtic getting out of their own half and over the halfway line.
While there seems to be some talk that Barcelona' cloak of invincibility has slipped, they remain a formidable outfit, whether they are depleted by injury or not.
Marc Muniesa, Dani Alves, Thiago Alcantara, Isaac Cuenca and Carles Puyol are sidelined by injury – as is long-term absentee Eric Abidal, who underwent a liver transplant earlier this year.
However, the Nou Camp outlet remain an intimidating entity on paper, boasting the likes of Lionel Messi, David Villa, Andres Iniesta and Xavi Hernandez; players more than capable of causing havoc.
Armstrong, though, believes that over the last 18 months many observers have watched and learned how to play against Barcelona, and it is here that he expects Lennon to have been taking notes.
"This is pretty much the same side as it was when everyone thought they were one of the best in the world," explained Armstrong. "They haven't changed, yet they lost their La Liga title and they lost their Champions League title. It isn't that they became a poorer team, but that teams studied them and attacked their weakness.
"Real Madrid, two years ago, even 18 months ago, couldn't live with Barcelona. Yet, all of a sudden they have found the measure of them.
"I actually thought that Real really should have won the last El Classico, which finished 2-2. After half an hour they could've been 3-0 up.
"It is no secret to anyone that Barca like the ball down, they move it quickly and they are always on the attack. But you can hurt them.
"In the last Classico match, Barca had 70% possession, but it was Real who had the better chances. If you do your homework – and I think that Neil will – you can get at them.
"Not, of course, that Celtic can go out and go hell for leather against them. It will need to be a mature and measured performance from them. They need to be prepared to see very little of the ball, and to be fully concentrated. If you get a sniff of goal, you need to be ruthless.
"Barca are quick on the attack, too, and it will need to be a solid defensive team game from Celtic. They've done it before in the Nou Camp. It is possible.
"They will need a little bit of luck, but who knows? If you do your homework and work hard you just never know. But Celtic will need every player to be switched on. One second not paying attention and it can cost you the game."
There is no pressure on the Parkhead side going into the game, although Lennon would not want to come away having been battered by Barca. The kind of scoreline that Celtic enjoyed against St Mirren at the weekend would have the potential to destroy their European confidence, but Armstrong expects Lennon to send his side out to make the most of the occasion.
"There is no expectation at all where Celtic are concerned," said Armstrong. "No-one in Spain expects them to come and do anything, and most would predict an easy evening for Barca. It's up to Celtic to try and upset their rhythm and get in amongst it.
"It's a fabulous arena to play football in, and getting a result in it would feel just fantastic.
"I bet that Neil has been working and thinking of this one for a few weeks now and he'll want his side to stick to a very specific game plan. But most of all you want to be able to take a look around you and enjoy it."