Matthew Upson believes Birmingham City need one more victory to be certain of retaining their Premiership status - and the defender hopes to secure the necessary points in the most unlikely of places.

The 25-year-old England international will be an integral member of Birmingham's rearguard at Chelsea on Saturday. Despite the Londoners being 13 points clear at the top of the table and unbeaten at home all season, Upson believes Blues can pull off a shock result at Stamford Bridge.

Birmingham, who drew 1-1 at home to Tottenham last Saturday, will be hoping Jose Mourinho's side are distracted by the return leg of their Champions' League quarter-final against Bayern Munich next Tuesday, despite taking a two-goal lead in last night's first leg.

But Upson knows Steve Bruce's side will have to perform extremely well and be positive going forward if they are to penetrate Chelsea's miserly defence.

Upson said: "We picked up a point against Tottenham and I think another win would see us pretty much safe. Chelsea will be tough but I would rather go there and have a real go at trying to win the game than lose 1-0 or 2-0 and not really turn up.

"I think that's the attitude we've got to take, to really push ourselves against some of the best players in the country.

"We have just got to go down there in the right frame of mind and with the kind of positive approach you need when you are going to a place where the team is playing really well."

Birmingham midfielder Stephen Clemence is doubtful for Saturday's match after missing the encounter with Spurs because of a bruised sternum.

Clemence, aged 27, sustained the injury in the 2-0 victory over Aston Villa last month and Blues' first-team coach Eric Black said: "Clem was devastated to miss the Tottenham game against his old club but he got a hard knock on his sternum. It hasn't gone away and has really knocked the stuffing out of him, so we'll have to see how he is on Friday."

Clemence's injury comes as his father Ray - who played in goal for England - battles prostate cancer.

Clemence senior was diagnosed with the disease this year and has since undergone an operation to remove his prostate. The results are positive, if not quite definitive.

Clemence junior said: "Dad has had his operation and is now waiting for a session of radiotherapy. The operation went well, but there is still a bit of cancer inside him. The radiotherapy will be for six weeks.

"It's not nice for him but, as a family, we are confident he will come through it.

"It is a case of us just being there for him when he needs us. I am sure there are times when he does get down but you would never know it.

"My dad is such a positive person. He would not have achieved as much as he has done in his life without that kind of attitude. He is a strong character and I am sure he will get through this."