He will take over the Sri Lankan side on December 20, when they face India in first of three Twenty20 internationals.
The Bangladesh Cricket Board (BCB) has suspended men's team head coach Chandika Hathurusingha due to inappropriate conduct by him during last year's ODI World Cup in India.
In the second innings not only Shanto (82), top-order batters Zakir Hasan (35) and Shadman Islam (35) also got starts they failed to convert, resulting in a heavy defeat.
Shakib Al Hasan, who was a lawmaker in the Awami League, was cleared by Bangladesh's new interim government last week to face Pakistan in a two-match Test series.
Ratnayake taking the role means that the future of current coach, Chandika Hathurusingha, is uncertain in the team.
'We know if we continue to play and give our best in the game, we can defeat any team.'
The Bangladesh Cricket Board on Monday cracked the whip on Shakib Al Hasan for indiscipline, handing him a six-month ban from all forms of cricket after the star all-rounder left for Barbados for Caribbean Premier League without the clearance from the Board.
Bangladesh wicketkeeper Mushfiqur Rahim will miss the remaining two one-day internationals against New Zealand with a hamstring injury.
The Indian team is currently playing fearless cricket but has been successful in scaring the daylights out of the opposition, Bangladesh head coach Chandika Hathurusingha said.
Bangladesh pacers have also been fortunate to have come under the tutelage of South African great Allan Donald and former West Indian pacer Otis Gibson.
Sri Lanka coach Chandika Hathurusingha on Monday termed India favourites in the triangular T20 series
Hathurusingha was also fully aware of the difficulty posed by his lack of red-ball cricket experience before the series.
Australian Shane McDermott has already been roped in as team's new fielding coach.
They might be the hosts but the Bangladesh team has been left baffled by the pitch for the one-off Test against India with their Sri Lankan coach Chandika Hathurusingha saying that he has never seen a track like the one in Khan Saheb Osman Ali Stadium in Fatullah.
Factbox on Saturday's World Cup match between Australia and Bangladesh.
A win would move Sri Lanka level with fourth-placed England on eight points and leave both teams with two matches to play -- in the case of the Lankans, ties against West Indies and India
Pace sensation Mustafizur Rahaman will not be a part of the Bangladesh squad for the one-off Test against India in Hyderabad from February 9-13 as he has not had enough game time post his surgery.
'Fully fit' Hossain fired up to face India in ODIs
Jamshed, who has played 48 one-day internationals for Pakistan, was suspended from all forms of cricket in February for violating the PCB's anti-corruption code.
Australia finally have the chance to bring some cheers to their fans after an egregious 2018 when Tim Paine's men take on Sri Lanka at the Manuka Oval from Friday with a series victory beckoning the beleaguered hosts.
The swashbuckling middle-order batsman scored 153, adding a record 78 for the final wicket with number 11 Vishwa Fernando, to guide his team to an epic one-wicket victory in the first Test against South Africa.
Nic Pothas appointed as interim coach of Windies
Curran went unsold in February's IPL auction but Kolkata Knight Riders recruited him for around $247,000 earlier this month to replace injured Australian paceman Mitchell Starc.
Bangladesh gearing up for their biggest battle against defending champions India in the cricket World Cup quarter-finals.
Former India captain Sourav Ganguly, who is a member of the Marylebone Cricket Club World Cricket Committee, will skip its upcoming meeting at Lord's on August 11-12.
Sri Lanka interim coach Nic Pothas said toss and the no-ball dismissal of Upul Tharanga by Jasprit Bumrah were the defining moments of the match.
After resuming on 384-4, the hosts declared their first innings closed after lunch. Kurtis Patterson, in just his second Test innings, was unbeaten on 114 after posting his maiden century and captain Tim Paine was 45 not out.
Bangladesh bowling coach Heath Streak wants young pace sensation Mustafizur Rahman to be looked after and supported well so that he can grow into a big match-winner.
Alastair Cook's side next travel to India, the world's top-ranked team, before hosting South Africa and West Indies in 2017 ahead of their ultimate challenge in a tour of Australia.
'It's Test cricket and (Shannon) is an emotional guy trying to do everything he can to win a Test match. Sometimes people say things on the field that they might regret'