On Tuesday night in the UEFA Champions League, at the Emirates Stadium in north London, Arsenal host Barcelona.Both teams are in the title race in their respective leagues, and it's arguably the tie of the round in Europe's premier competition.But to look at the two performances these sides put in on Saturday, you would never have guessed it.Arsenal slogged through their FA Cup game with Hull City, unable to break the deadlock, meaning a replay will be needed after the 0-0 draw.Arguably only two of the starters from this game, Laurent Koscielny and Per Mertesacker, will form part of Arsene Wenger's XI in midweek, though.Alexis Sanchez, Olivier Giroud and Alex Oxlade-Chamberlain were called from the bench, and they sparked life into Arsenal, with their second half showing a little more like what we can expect in the Champions League.Barcelona were also significantly below par.And given they put out a side which seemed close to full strength, with Lionel Messi, Luis Suarez and Neymar up front, Arsenal might be tempted to take the 2-1 win away at Las Palmas as a sign of weakness. That would be wrong.Various factors contributed to Barcelona's bad performance in the Canary Islands. Factors that will not affect them in London, under the lights.For one, there were two notable absences. Gerard Pique was rested, with Jeremy Mathieu stepping in, while Sergio Busquets was suspended and Sergi Roberto took his place.Neither of those two replacements are awful, but likewise neither can come near the level of the men whose shoes they had to fill.Pique and Busquets are part of Barcelona's spine, both of whom help to build attacks from the back and are the two most important parts in cutting out an opponent's own moves.The return of those two will transform Barcelona when they take on Arsenal.Then there was the condition of the pitch. After days of bad weather and a torrential storm, it wasn't the greatest surface to play on. By contrast, the Emirates is pristine, and that plays into Barcelona's hands.Luis Enrique's Barcelona also have two modes. They have performances like this, and then another level, three gears higher.Against Las Palmas they suffered in defence, with the hosts creating several chances, and without Pique and Busquets, Messi saw less of the ball and was not involved as much. They are a funnel from which the team's play starts.In the 6-1 win over Celta Vigo we saw both sides of Barcelona. They weren't playing particularly well until the final 20 minutes, when they somersaulted up to dizzying heights.Las Palmas away, at 4 p.m. local time, in a league match to go nine points clear of Atletico Madrid and 10 of Real, doesn't have the same pull as Tuesday's clash.With the eyes of the world on the trident, and what is likely to be the "Gala XI" (Marc-Andre ter Stegen, Dani Alves, Pique, Javier Mascherano, Jordi Alba, Busquets, Ivan Rakitic and Andres Iniesta) behind, Barcelona will improve.Spanish newspaper Diario Sportis confident of that. Its front cover on Sunday ran: "Wenger, don't get too excited, we were snoozing."And it will probably prove to be correct. Anyone who has seen this Barcelona play in a big game will know they are far removed from the team we witnessed on Saturday.Or didn't witness, if you were Wenger. He left his post-game press conference telling journalists he was going home because "Barcelona play at 5:30 p.m., and I want to watch them."Unfortunately, he got the times wrong, it was 3 p.m., and Luis Suarez had already scored the opening goal by that point.In the end it didn't matter; this Barcelona display won't prove too useful for the coach to analyse. The Clasico win over Real Madrid, the 6-1 humiliation of Roma and the 7-0 destruction of Valencia. Those will be more useful.Not because Barcelona are going to have things all their own way against the Premier League challengers. But just because that's big-game Barcelona. And Wenger should expect to see them on Tuesday.Any quotes taken firsthand. Click here to read full news..