Manchester United legend Paul Scholes believes Arsenal's failure to shine against top clubs is down to lack of mental strength.

The Gunners' record against the top four has been woeful in the past few seasons and their poor form has cost them a chance to win the league title. In addition to this, the north London club struggled in the Champions League as they made it to the last four only on two occasions for over a decade.

Arsene Wenger takes his side to Germany as they take on Borussia Dortmund in the opening fixture of Europe's elite club competition at the Emirates on Tuesday.

"They always qualify and always seem to get through the group. The only problem with Arsenal is when they meet top teams, they don't seem to have the consistent level of mental strength to get through it," Scholes explained, as quoted by the Daily Mail.

Arsenal's league rivals Liverpool return to the Champions League after five years of absence. The Reds host Ludogorets in their opening fixture at Anfield on Tuesday. They are pitted against reigning champions Real Madrid and Basel in Group B.

Scholes says Brendan Rodgers' side are the dark horses to win Europe's most elite competition. The Old Trafford star also heaped praise on the Liverpool manager for helping the Merseyside club return to European football.

"Liverpool are the dark horse of the competition this year. Brendan Rodgers has done a fantastic job. The style of play he's adopted is exciting to watch and the players seem to have taken to him. I feel they will do well with the players they have," the former United midfielder said.

The former England midfielder has backed Mario Balotelli to shine for Liverpool and fill in the void left by the departure of Luis Suarez for Barcelona.

"The big advantage they have is a home crowd. Anfield is always a hostile place to go, which is something Manchester City lack. He [Suarez] is a great player, but don't forget they've signed Balotelli who, on his day, can be a match winner too," Scholes concluded.