The Manchester United striker Dimitar Berbatov has become the centre of controversy in his native Bulgaria after his angry agent suggested the player could retire from international football because of criticism of his performances.

Last month several players, including Berbatov, were lambasted by the Bulgarian Football Union vice-president Yordan Letchkov for showing little enthusiasm for their national team. And when Berbatov asked to be substituted 30 minutes into last night's 6-1 defeat in Serbia, the commentator of Bulgarian TV channel Canal 1 repeated the accusation and suggested Berbatov was a liability to his country. The player's agent, Emil Dancev, reportedly rang the broadcaster in a rage at half-time to complain about the comments and hinted that his client may refuse to play for Bulgaria again.

Bulgaria's manager, Plamen Markov, explained after last night's match that Berbatov had asked to be replaced because he was suffering from a "slight injury" and Dancev today confirmed that the striker is set for a spell on the sidelines. "According to Manchester United's medical staff Berbatov will be recovering for between seven and 10 days," he said.

Markov is himself under pressure following the crushing defeat, which has lent credence to rumours that many of the players, including Berbatov, want the manager to be dismissed. However, the 51-year-old former CSKA Sofia manager last night insisted he will not step down.

"I don't know why they're always talking about resignation," he said. "I doubt that coaches' resignations will sort matters out. Bulgarian football doesn't have the potential that we want to have. But I'll continue my work and I hope that we will achieve some better results."

Markov previously quit as coach after the Euro 2004 finals in Portugal where Bulgaria suffered three defeats, but was reappointed in January. Bulgaria have managed only three lacklustre draws in their 2010 World Cup qualifying campaign, and lie in third place in their group, four points behind the Republic of Ireland.

Local media blamed Markov for what has been described as a "ridiculous and unforgivable loss" during which Serbia, in addition to hitting six goals, missed two penalties. Vice-president Letchkov, however, again attributed the fault to the players and expressecd his support for the manager. "He has our backing and I see no reason to discuss this issue," said Letchkov.

The moment that Rafael Nadal, the world's leading player, pulled out of the Davis Cup final in the coastal city of Mar del Plata - and the rumours coming out of Spain are that the right knee problem, despite assurances to the contrary, may be much more serious than tendinitis - the chances of Argentina winning the trophy for the first time increased hugely. Only 12 nations have ever won the Davis Cup, and good fortune has deemed that the South Americans have played all their ties at home this year, the significance being that they have not lost in Argentina for a decade.

This competition, played annually, comes under perennial criticism for crowding an already over-crowded season, yet it survives because, essentially, the players love it. Some may opt out from time to time but inevitably they are drawn back by the prospect of playing as a team in front of crowds who are able to release the shackles of tennis convention and support their country with partisan glee.

Such support can get out of hand. Opponents' double faults and missed shots are cheered, while mirrors have occasionally been employed to dazzle the opposition. However the International Tennis Federation, the sport's governing body, has adopted powers to punish the overly enthusiastic fans by docking points, games, sets or even the tie itself.

Without doubt the 11,000 spectators in the Islas Malvinas stadium will match anything the Argentine football crowds routinely manage, and peace and quiet is something the Spaniards will not experience this weekend, unless they still the baying hordes by dominating this final, and that seems unlikely with Nadal absent. The Argentines play the majority of their home ties on clay, though on this occasion, mindful that Nadal is the four-times French Open champion and having to decide the venue prior to his injury, they selected an indoor hard court. It now looks more of a risk although in David Nalbandian they have one of the finest indoor players in the world. Initially at least the Argentine team were none to happy at having to play outside the capital Buenos Aires.

Both countries are among the powerhouses of modern men's tennis, with Spain currently having 14 players in the top 100, and Argentina nine. It was only a matter of time before the Spanish won their first Davis Cup final in 2000, in Barcelona against Australia, a victory repeated four years later in Seville when Nadal, then only 18, made his singles debut, beating Andy Roddick. Now, after losing the final against Russia on Moscow two years ago, Argentina feel their moment has arrived.

If there are doubts then they centre on the inexperience of 20-year-old Juan Martín del Potro, and the occasional contrariness of Nalbandian. Del Potro was in Shanghai last week making his debut in the season-ending Tennis Masters Cup, having reached the top 10 for the first time this year, and replacing Nalbandian as his country's No1 player. At least he has not had to make the transition from indoor to clay, though he may still be feeling a little travel weary.

As for Nalbandian he is capable of beating any of the world's leading players, while at other times being inexplicably vulnerable. He has had a poor year in the slams, though his form and focus improved sharply towards the end of the season. It appears he has partly sacrificed his own ambitions in order to lead his country to victory this weekend.

Spain without Nadal remain strong, though lacking the obvious thrust and charisma. Much, as so often is the case, may depend on the doubles. In the singles Spain opted for the left-handed Feliciano López, who is a natural serve and volleyer, and David Ferrer, badly out of form, in Friday's opening singles. The Argentine doubles team looks set to be Agustin Calleri and Jose Acasuso, who have both been working hard on their service returns with the prospect of facing the two Spanish left-handers in Lopez and Fernando Verdasco, who play regularly in ATP tournaments.

Opening singles: David Nalbandian v David Ferrer; Juan Martín del Potro v Feliciano Lopez.