Henman is prepared to shoulder the burden

British players have learned not to take results for granted, whether facing Pete Sampras or Danai Udomchoke. That is reassuring, because injuries and form have narrowed this weekend's Davis Cup contest against Thailand to a whisker.

The outcome, and continued participation in the World Group, may hinge on Tim Henman's dodgy right shoulder. The British No 1 says the injury has responded so well in practice since he had an injection 10 days ago – "partly anaesthetic, strongly anti-inflammatory" – that he is prepared to compete in three best-of-five-sets matches. "I feel confident," Henman said, "but I'd be lying if I said there was no doubt."

That element of doubt, along with the form of Paradorn Srichaphan, the Thai No 1, has given the visitors the whiff of a victory in the offing, a sense of purpose which has grown from the moment they arrived here and discovered that Greg Rusedski, Britain's other world-class player, had cried off because of a foot injury.

"We have a chance now to get closer," ventured Srichaphan, whose summer has shimmered with triumphs against Andre Agassi at Wimbledon, Marcelo Rios in Washington, Tommy Haas in Long Island and Marat Safin in Tashkent. The world No 31 also pushed Rusedski to five sets in the second round of the United States Open.

Competing for a place in the 16-strong World Group for the first time, the Thais can almost see parity with their opponents. Srichaphan may be short of Henman's achievements, but he is fighting fit and dauntless: "I always like to play in front of big crowds on show courts."

If Henman's shoulder is as sound as he believes it to be, the balance of the tie will swing in Britain's favour. Provided, that is, Martin Lee, who replaces Rusedski in the singles, and Miles Maclagan, who takes Rusedski's place in the doubles, prove themselves to be better than Srichaphan's team-mates. Roger Taylor, Britain's captain, lightened the mood with a touch of humour, saying: "Tim's fine – it's the rest of the team I'm worried about."

Henman, the world No 5, opens the proceedings at noon today against Udomchoke, the Thai No 2, ranked 204. Although we hear that world rankings count for little when players represent their country, and also that top 10 players on the ATP Tour can come unstuck against an opponent in the top 250, we trust that Henman, shoulder willing, will give the team a winning start.

Lee, ranked No 168, falls into the above category of a lesser light striving for full beam when he plays Srichaphan in the second of today's singles. The left-hander from Worthing has practised with Srichaphan in the past, but this will be their first match.

Maclagan, who will be 28 next Monday, is being asked to play Rusedski's part in extending Britain's unbeaten record in six doubles rubbers. Henman said he felt comfortable with Maclagan in his regular partner's absence. Maclagan recalled that in their only previous doubles match, at under-16 level, he was told off for staying back behind his serve. He will need to step up against Narathorn Srichaphan (Paradorn's older brother) and Wittaya Samrej in what could be the pivotal rubber. If the tie is live on Sunday after Henman has played Srichaphan, all eyes will be on Lee and Udomchoke, men of destiny.

DAVIS CUP World Group Qualifier: Great Britain v Thailand (NIA, Birmingham, GB names first): Today (noon start): T Henman v D Udomchoke; M Lee v P Srichaphan. Tomorrow (2pm): Henman and M Maclagan v Srichaphan and V Samrej. Sunday (noon): Henman v Srichaphan; Lee v Udomchoke.