It’s hard to believe it’s been four years since Celtic beat Barcelona in Parkhead. It’s also hard to believe that only four of the Barcelona starting lineup from that day are still at the club.

Only Jordi Alba, Javier Mascherano, Andres Iniesta and Lionel Messi remain from the Barcelona starting line-up that night, plus Gerard Pique who came off the bench.

It’s also a completely different Celtic team, of course, and that was the last time a Celtic side has managed to qualify for the knockout stages of the Champions League. Since then, Celtic have been pottering around the play-off rounds and languishing in the Europa League, for the most part.

But the arrival of Brendan Rodgers has changed the feel of the club. New, exciting players have arrived, and it now feels like Celtic have a manager and a playing squad befitting of a club with a European Cup in the trophy cabinet.

But no matter how big you are, playing Barcelona is a difficult task. They are without a doubt one of the best teams to ever play the game, their front three is perhaps the most fearsome ever assembled, and they enjoy an embarrassing amount of possession even against clubs who are considered amongst Europe’s elite.

And yet, Barcelona have lost three of their last six home games in the league, the latest to newly-promoted Alaves at the weekend. Can Celtic exploit that poor form and grab a result at the Camp Nou tonight?

Here’s five things they need to do to get a result against the best team in the world...

Have a solid gameplan and stick to it

Celtic Press Conference

Barcelona are coming off the back of a fairly embarrassing defeat at the Camp Nou.

The defeat is, of course, mitigated by the fact that Barcelona are always at their most vulnerable after an international break (some very key players have to travel to South America and back) and the fact that Barcelona rested most of those players anyway with the Celtic game in mind.

That makes it harder for Celtic than it was for Alaves, of course, but they came to the Camp Nou with a solid gameplan and they stuck to it. Celtic need to do the same.

It sounds easy, simple, but it’s not. There is a natural tendency to be overawed by the occasion, by the huge stadium, by the players you’re playing, but keeping your discipline is half the battle of getting a result in Barcelona.

Don’t get dragged out of position by dummy runners, make sure you stick to your position, identify real danger rather than tracking a man who poses no threat. It’s all easier said than done, and when you don’t have the ball the whole game, the fatigue - both mental and physical - take their toll. It’s not easy, but sticking to it for 90 minutes is the key to success.

Cut down space between midfield and defence

Celtic v Rangers - Scottish Premiership

It’s one thing having a game plan, but you also have to have the right gameplan!

The most effective against Barcelona - as Alaves this season and Atletico Madrid in last season’s Champions League proved - is to close down the space between the midfield and the defence.

That space is where Messi and Iniesta want to play. They slip in between midfield and defence, defenders don’t want to step out and midfielders don’t want to step back. That leads to confusion but also to players getting dragged out of position: fertile ground for a clever run and a threaded pass.

Play five defenders?

Celtic v Astana - UEFA Champions League Third Qualifying Round Second Leg

One of the ways Alaves ensured this space was covered was by playing with five defenders. That meant there was always a back four, even if one defender stepped out to track a player trying to play in between the lines.

But playing with a back five means being very disciplined.

Three central defenders can cut down space, but that also creates extra gaps that can be exploited between defenders. Whereas with a back four you only have spaces between two centre backs and full backs, playing with an extra defender creates an extra gap that can be exploited.

Whatever the formation, being disciplined and making sure that gaps aren’t wide enough for Barcelona to do anything with them is essential.

Make the right decisions on the counter attack

Celtic v Rangers - Scottish Premiership

It’s all well and good defending, but you can’t do it for 90 minutes.

Aside from the fact that Barcelona will have more time to pick an opening if you try to defend the entire game, you’ll also get too tired mentally and physically. You need to support the attack.

Players must be prepared to bury themselves because without the ball they are going to be running the whole game anyway, but they’ll also have to be prepared to take it forward when they get it. Making the right decisions on the counter attack isn’t only about creating a chance and landing a killer blow, but it’s also about taking the pressure off for a few minutes.

Making the right decisions on the counter attack isn’t only about creating a chance and landing a killer blow, but it’s also about taking the pressure off for a few minutes.

Exploit Barca’s home weakness

FC Barcelona v Liverpool - International Champions Cup

If you do defend with discipline, and you do counter attack with a clear head, there might be a chance to nick a goal.

Barcelona have, after all, lost three of their last six La Liga games at the Camp Nou, so there’s a weakness to exploit.

Against Alaves, new goalkeeper Jasper Cillessen looked fragile and with Marc-Andre Ter Stegen just returning from injury, Luis Enrique may not feel it prudent to risk the German stopper against Celtic.

The departure of Dani Alves also leaves a gap that Celtic might be able to exploit - Sergi Roberto is the jack-of-all-trades in the Barcelona squad, but not a natural right back, whilst Aleix Vidal hasn’t looked convincing since his move last summer, though he has only been able to play for the club since last January due to the club’s player registration ban.