West Ham's Matthew Upson believes he is the number one contender to partner John Terry if Rio Ferdinand's injury problems resurface at the World Cup.
England captain Ferdinand has suffered back and groin problems this season.
And competition for the centre-back slot has seen calls for Tottenham's Ledley King and Michael Dawson to join the squad in South Africa.
"Going on the last few internationals I'd have to say I do feel like I am the next in line," Upson told BBC Sport.
"But football changes very quickly so you can never rest back and take that for granted, so I think it's important you keep on top of your game and keep wanting to improve to secure your place."
Capello's message to England fans
Ferdinand has played 19 matches for Manchester United this season, plus another seven for England, but his season has been a stop-start affair because of a succession of injuries.
Under England boss Fabio Capello, Upson's emergence as Ferdinand's replacement has seen the former Birmingham defender start nine of England's 17 matches since the beginning of the World Cup qualifying campaign.
And although he is still regarded as playing second fiddle to former England skipper Terry, England have been defeated only once when Upson has featured - the 1-0 loss in a friendly to Brazil.
"I've really enjoyed playing and it has been a good run of games ever since Mr Capello took over as manager so I have enjoyed every minute of it," Upson told BBC Sport at the launch of the Football Association's England Football Day.
"Getting back into playing football at this level is why I get out of bed in the morning. It drives me on and I've really enjoyed being in the squad again."
Upson's form for England has come at a time when the defender has suffered testing times at club level.
Six straight defeats in February and March had West Ham staring relegation in the face and they only managed to effectively secure their Premier League status last Saturday after beating Wigan.
If he's not happy with something then quite rightly he tells you and that level of discipline needs to happen and I think it brings the best out in the group
Upson on England boss Fabio Capello
The players, as well as manager Gianfranco Zola, have come under fire from co-owners David Sullivan and David Gold and the latest outburst by Sullivan saw him made it clear that the entire Hammers squad - with the exception of Scott Parker - was available for the right price.
Declining to answer questions about his future, the Hammers skipper said: "It has been a challenge to cope with the situations on and off the field at the club, it hasn't been easy at times but if anything it makes you a stronger character.
"Having had that kind of adversity throughout the year, hopefully it will be nice to get some different kind of problems and a different feeling with England.
"It's been a difficult time at West Ham, we're safe now and I'm pleased that that's happened and hopefully the club can build on that. But it will be nice to go into the tournament - hopefully at the other end of the scale."
Upson said he still harboured ambitions to play in the Champions League again, having tasted European football when he was a youngster at Arsenal.
And he said he had responded to Capello's disciplined approach to give him belief to play at the highest level.
"Capello knows what he wants and if players can't deliver that to him then he lets you know," Upson added.
"Whether it's an arm around the shoulder to be told quietly or if it's in front of everyone in a meeting, he's got his style and his fashion of getting his message across and at times it's not for the faint-hearted.
"If he's not happy with something then quite rightly he tells you and that level of discipline needs to happen and I think it brings the best out in the group.
"He likes to see players work hard; he likes to see you play with confidence, belief and with discipline and that's the key thing he has brought to the team.
"I'm not just talking about behaviour, I'm talking about tactically out on the pitch and I think that's a trademark of his management.
"He has huge respect throughout the squad and throughout the football world. His winning capabilities have been shown in the past and it would be great to see those capabilities at international level for England."
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