By Spain correspondent Miguel de Souza

Lionel Messi has identified Alexis Sanchez as the biggest obstacle to Barcelona reaching the Champions League quarter-finals.

The Spanish giants are strong favourites to progress past Wednesday’s second-leg showdown with Arsenal at Camp Nou after winning 2-0 in the last-16 first leg in London three weeks ago.

Arsene Wenger has admitted that Arsenal have only a “five per cent chance” of upsetting the odds and ending Barcelona’s 37-match unbeaten run in all competitions.

Messi, who scored both of Barcelona’s goals at Emirates Stadium, told the Spanish media that his team are aware that their opponents have some quality players, including one former team-mate.

“Of course we know the danger that Alexis Sanchez can bring but that is only one of many top quality players they have,” Messi said.

“The style they play is the most similar to that which we play at Barcelona and for that we have a lot of respect for them.”

Sanchez had an outstanding first season at Arsenal after ending his three-year spell at Camp Nou in the summer of 2014.

The Chilean has been less effective in the current campaign, but his 82 appearances for the Gunners have still yielded 36 goals and 20 assists.

In other Arsenal news, Aaron Ramsey is facing a lengthy spell on the sidelines with a thigh injury.