Sri Lanka will start the test series against New Zealand this week already two down in a rubber when they need plenty to go their way to have a chance of success.

Having had bustling fast-medium bowler Dhammika Prasad ruled out by a back injury, they've now had wicketkeeper Kusal Perera rubbed out after testing positive for a banned substance.

Perera's story is he took treatment for a bite on a foot and was caught in an International Cricket Council random test but "he says he's not taken any form of drugs", Sri Lanka's coach Jerome Jayaratne said.

His B sample hasn't been checked yet but Jayaratne is preparing for the worst.

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"I think it'll have quite a big impact. He's our main wicketkeeper and, at No 7, is a dashing batsman who can turn things around. It's a massive dent," he said.

Jayaratne said the players had been kept up to speed and told to talk with the team physiotherapist before taking any medication - "even if it's a Panadol".

Perera has played three tests (averaging 33.8), and 51 ODIs. Considering Sri Lanka are starting life without their champion batsman Mahela Jayawardene and Kumar Sangakkara, the double loss is precisely what they didn't need.

"We have to regroup. It's a team in transition, so it's not an ideal situation losing two prime players who we had a lot of hopes in for the tour," Jayaratne said.

Replacement Kaushal Silva arrives in Dunedin tomorrow but talented Dinesh Chandimal will keep wicket in the first test, and is one of the players Sri Lankan captain Angelo Mathews will rely on to step up with a big contribution in the middle order. He averages an impressive 45.6 from 23 tests.

How much success their veteran left-arm spinner Rangana Herath will get from the pitches in Dunedin and Hamilton is a moot point. But he's a tidy and highly successful operator.