Sri Lanka will play a full-strength team when they tackle Afghanistan in the World Cup on Sunday, with skipper Angelo Mathews insisting it would be disrespectful to underestimate the tournament minnows.

The 1996 champions lost their opening fixture in Pool A, as did Afghanistan, and that defeat make Sunday's clash at the University Oval all the more important to Sri Lanka's hopes of making the quarter-finals.

"We are playing the full team. Every game is important for us, whether you play Afghanistan or Australia, every game is important, so we'll take every single game very seriously, and we'll play the best XI possible on that day," said Mathews.

His plan to play his strongest side hinted at a reprieve for key swing bowler Lasith Malinga who was smashed to all parts of the Hagley Oval in Christchurch last Saturday in his team's 98-run loss to New Zealand.

Malinga, 31, ended with figures of none for 84 off his 10 overs as the Black Caps piled up 331 for six.

The loss to New Zealand also saw Sri Lanka commit a series of fielding errors, with the dangerous Kane Williamson one beneficiary when he was dropped by wicketkeeper Kumar Sangakkara off the first ball he faced before going on to post 57.

"We've done a lot of hard work with our fielding, but it's just the consistency level -- one game we'll be extremely good, the next game we've dropped our standards a little bit," said Mathews.

"It's a lack of concentration obviously. When you do mistakes, obviously you lose your concentration, and that split-second can turn the game around."

Afghanistan lost their World Cup opener against Bangladesh by 105 runs when, chasing a target of 268, they were dismissed for 162 at Canberra's Manuka Oval on Wednesday.

But Mathews is not expecting the World Cup debutants to roll over on Sunday.

"They're a very dangerous team. You can't take them lightly because they can upset a team, and they've got nothing to lose," the captain said.

"We can't just run through them. We've got to fight really hard from ball one to ball 300 probably, and fight it out and just take it as a Test-playing nation."

Afghanistan seamer Mirwais Ashraf, who took two for 32 in the defeat by Bangladesh, admitted Wednesday's had been a brutal introduction to World Cup cricket and that they had been punished for basic errors.

Their naivete was illustrated in the third over when Bangladesh opener Tamim Iqbal edged a ball from Hamid Hassan and was caught behind.

The umpire gave Tamim not out and the Afghans ran out of time in which to review the decision.

"We are new in this big event," said Mirwais. "It was a little bit disappointing, that decision," said the 26-year-old.