Arsenal will be without their Danish striker Nicklas Bendtner for tomorrow's Champions League game against Olympiakos after the striker was involved in a car accident.

The 21-year-old was driving along the A1 yesterday morning, towards South Mimms, when his car left the road.

It is understood no other vehicle was involved in the incident and a Hertfordshire police spokesman said: "We were called at 10.15am to a report of a single vehicle road traffic collision. A black Aston Martin vehicle had left the road. The driver was not seriously injured."

His manager Arsène Wenger said today: "Nicklas did not practise because he had a car accident. Fortunately there was no real long-term damage, but he was bruised and we thought it better he did not train. He should be back for Sunday's game [against Blackburn]."

The East of England Ambulance Service said he had a "very lucky escape" suffering a pain in his shoulder and grazes on one of his knees.

"When the ambulance crew arrived at the scene they found a car which was badly damaged after it collided with the hard shoulder fence and a tree," a spokesman said. "A man who we believe to be 21-years-old received minor injuries. Following a check over by paramedics, he did not require to go to hospital."

Theo Walcott is expected to return from a back problem in time for the weekend, but Denílson is set for up to two months on the sidelines with a fracture to his back.

The goalkeeper Manuel Almunia, meanwhile, is still troubled by a chest infection so Vito Mannone will continue in his place following the Italian's man-of-the-match display against Fulham on Saturday.

Samir Nasri [leg], Lukasz Fabianski [knee] and Johan Djourou [knee] remain out.

One man who will almost certainly start against Olympiakos is Robin Van Persie. The Dutch striker became the centre of attention when he scored Arsenal's winner against Fulham on Saturday evening after earlier admitting he occasionally dives for penalties.

Wenger, though, was quick to defend the player yesterday. "Sometimes when a striker is fouled, he wants to make sure the referee sees that, which is what basically Robin was talking about," said the Frenchman. "He wanted to show there is a difference between what people call diving and being fouled.

"In fact, the television showed a great example of it at Manchester United when a penalty was not given when [Patrice] Evra fouled Van Persie 100%. He had to go down, but when you go down, you make sure the referee notices you have been fouled.

"There is a trend all over Europe to give less fouls and less penalties than before – at Italy there was a stage when they gave a penalty every time somebody collapsed."