Birmingham midfielder Sebastian Larsson admits it would be a surprise if his side won Sunday's Carling Cup final against Arsenal at Wembley.Larsson, 25, spent six years at Arsenal before moving on loan to Birmingham in August 2006, which led to a permanent move for the Swede."A few of the lads have said, you never know if these opportunities are going to come round again, hopefully they do many times again," Larsson said."We've got to do our utmost to take the opportunity and make sure we get the trophy. We know we are underdogs and it would be an upset to a lot of people if we won. That's our aim and that's we are going to make sure we leave Wembley as the Carling Cup winners."Larsson's teammate, striker Cameron Jerome, believes his side can pose a real threat to Arsene Wenger's men."Everyone knows what a great side Arsenal are and how much they love to play football, but every time we've played them, we've matched them, especially at St Andrews," Jerome said."We're going to Wembley, and it's a neutral venue, and it's a cup final where anything can happen. Arsenal are obviously the favourites, but we are calm and we're confident and we think we can cause an upset."Meanwhile, Birmingham manager Alex McLeish has refused to rule Belarusian midfielder Alexander Hleb out of Sunday's final.Hleb suffered a knee injury during Birmingham's FA Cup victory against Sheffield Wednesday over the weekend and left the ground on crutches.But scans cleared the 29-year-old - also a former Arsenal player - of ligament damage and McLeish admitted there is an outside chance of him appearing at Wembley. "It is not a ligament problem. Alexander had a scan yesterday and it is just severe bruising," McLeish said."He is seeing the surgeon in London today and I haven't ruled him out for Sunday.""Alex has great skill and massive experience and it is something I'd like to be able to call upon at some stage in the game if he is fit."