Chelsea boss Andre Villas-Boas feels Porto can upset Manchester City in their Europa League clash.

Villas-Boas left Porto for Chelsea at the end of last season after winning the second tier European competition.

"I see great possibilities for FC Porto when attacking. City is exposed more, they're making some mistakes, but they have great individual talent who can make a difference. It will be very difficult.

"The Dragao atmosphere will be very difficult for City. Their stadium in Manchester, the environment is not as aggressive and this can be beneficial for FC Porto with the result obtained at home," said AVB.