Senanayake, 29, was the team's top spinner in the first half of 2014, regularly bowling in the Powerplay and at the death, while also posing a menace during the middle overs.
His new action - which is said to have a higher release point than before - has served Senanayake well in domestic cricket so far. He has five wickets from three List A games for Sinhalese Sports Club, and was also effective in the Mercantile Cricket Association tournament in August, when he first bowled with his remodelled action.
"It's hard to gauge how effective he is when he hasn't played international cricket yet," Atapattu said. "The domestic cricket here is played at a different level. The big challenge is to perform with all the pressures of an international match. I have a lot of faith in Sachithra. Having seen him over the years, I know he's a tough character, and a player that is well-liked in the team. I trust that he'll be the same bowler, with a different action."
Senanayake may even play in the fifth ODI on Wednesday, after being drafted into the side after Rangana Herath pulled a hamstring at training on the eve of the match. He was observed closely in the months he was banned from international cricket, with the board devoting significant resources to his remedial work, and eventual redemption.
"When he was doing work with his action, we had cameras covering the matches that he played. He was comfortable then, and though I know that it is a different challenge and different pressure bowling on the international stage. But knowing him, I think he'll be up for it. He was enthusiastic to get back as soon as he can."
Sri Lanka's World Cup preparation suffered setbacks during Senanayake's five-month ban. The selectors trialled Suraj Randiv in Senanayake's place, while the opposition's Powerplay overs - when Senanayake had routinely bowled - were an area of weakness, particularly in the tour of India. Senanayake was integral to Sri Lanka's limited-over successes in the first half of 2014, and Atapattu suggested the ban had come at a bad time for the team.
"People have questioned the timing of the ban," he said. "Everyone was preparing their squads for the World Cup, and you need your best spinners in operation in those conditions. It would have been much better if the ban came after the World Cup or much earlier than it did. But if it had to come, it had to come. In our case, we got through it. Our main concern was Sachithra - we've got the good news today. We'll proceed with whatever plans we have."
Andrew Fidel Fernando is ESPNcricinfo's Sri Lanka correspondent. @andrewffernando