World Football: 5 Teams on Upset Alert This Weekend

International week is finally over, and now it's time to turn our attention back to the domestic leagues.

All the big clubs will be in action over the weekend, but not all of them will win their matches. Which ones are on upset watch this week?

Read on to find out who we picked, and leave your own ideas in the comments section below.

The Gunners host Southampton on Saturday in the English Premier League. Southampton currently sit dead last in the league, the only club yet to have picked up a point.

So what's the danger?

The Saints actually held second-half leads against both Manchester City and Manchester United before losing, 3-2 in both cases. With just two goals scored this season, Arsenal might struggle to overturn a deficit, should they face one in the second half.

Then again, Arsenal haven't allowed a single goal yet, either.

Southampton are much better than their record indicates, but Arsenal are tough to beat at home and their defense has improved greatly. Plus, Santi Cazorla and Lukas Podolski showed signs of a new understanding two weeks ago against Liverpool.

Chance of upset: 25 percent

Atletico enjoyed a thrilling run to the Europa League title last season. They followed that up with a UEFA Super Cup rout of Chelsea nearly two weeks ago.

Diego Simeone's team returns to La Liga action this weekend, and the fixture list would seem to have presented a favorable opponent in Rayo Vallecano. Widely tipped for relegation this season, Rayo have started the season in strong form with wins over Granada and Real Betis and a draw with Sevilla.

Atletico have only played twice in the league, and it's been nearly three weeks since their last match. Colombian striker Radamel Falcao is a threat to take over any match he plays in, but might Atletico show a bit of rust against Rayo?

Chance of upset: 20 percent

Ajax, the two-time defending Dutch champions and the most successful club in Holland, started the season with two impressive wins and two draws.

Huge victories at NEC Nijmegen (6-1) and home to NAC Breda (5-0) have been tempered by draws with AZ Alkmaar and Heerenveen.

RKC Waalwijk, meanwhile, started the season with a 3-2 upset victory over PSV Eindhoven. Rodney Sneijder and Teddy Chevalier have scored two goals each as Waalwijk have climbed to fifth in the table.

That's just one spot behind Ajax. They'll never have a better chance to overtake the famous old Amsterdam club.

This could go either way. Ajax might record its latest blowout win or slump to another draw.

Chance of upset: 10 percent

In La Liga, Barcelona sit atop the table with three wins and nine points from their opening three matches.

Up next is a trip to Getafe and…honestly, this shouldn't be a tricky trip at all. The only reason Barca show up on this list is because Getafe beat Real Madrid 2-1 three weeks ago.

Anyone think Getafe will sneak up on Barca?

No, I don't think so either.

Chance of upset: 5 percent

Olympique Marseille have made headlines early in the season for winning their first four matches in France's Ligue 1 and for signing bad-boy English midfielder Joey Barton.

Elie Baup's team started the season with wins over Stade de Reims, Sochaux, defending champions Montpellier and Stade Rennes. Forward Andre-Pierre Gignac has three league goals already, including the winner against Montpellier.

Next up is a trip to AS Nancy on Sunday. Nancy beat Brest at home on the first day of the season but lost on the same ground to Toulouse two weeks later.

So can Marseille keep up their dream start to the season?

Chance of upset: 25 percent

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