Forecasts predict persistent rain in Cardiff, which could play havoc with Afghanistan's bid to get their first win in this year's tournament.
Naib's team were given a harsh lesson by Australia, who cruised to a seven-wicket win in the opening game for both teams in Bristol on Saturday.
But Naib believes his team have a better chance of success against Sri Lanka, whom they beat by 91 runs in last year's Asia Cup, if the contest is reduced from the scheduled 50 overs-per-side due to the weather.
"It was also predicted for today, but it didn't rain so much," Naib told reporters.
"Tomorrow we just see what's the weather. I think maybe the weather will be the same. So if we can reduce the overs it will be much better for us."
Despite the defeat against Australia, Naib says Afghanistan were encouraged by parts of their performance and he hopes to build on that in the Sri Lanka match.
"We've got to be positive. If you look, we missed out on 12 overs in the previous game, yet we scored 200-plus," Naib said.
"If you have wickets in hand, so maybe the score is 300-plus something."
Sri Lanka were dismissed for a paltry 136 by New Zealand in their first World Cup match in Cardiff and Naib plans to prey on those batting weaknesses.
"I saw the Sri Lankans play on TV. They lost a few games in the last two years and they're struggling in ODIs," he said.
"Yeah, we have the opportunity to do well against them," added the skipper.
"But they are also a good team and we cannot it take easy. We can try to score big. If we play 50 overs maybe it will be difficult for them."
Naib also declared pace bowler Hamid Hassan fit to face Sri Lanka.
"Hassan was hit by the ball (in the last game) but he's feeling well," he said