Lehmann ended weeks of speculation over Clarke's participation in the ICC's showpiece event, which begins on February 14.
"Definitely," was Lehmann's reaction when asked if Clarke would be fit in time to lead Australia in the World Cup.
"He's (Clarke) ahead of schedule," he added.
Clarke has time till Australia's second pool match of the World Cup against Bangladesh on February 21 to prove his fitness. But Lehmann hoped that Clarke would make a comeback much earlier.
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Clarke is set to play for Cricket Australia XI against Bangladesh in a One-Day practice match at Allan Border Field, although he would only bat and do light fielding.
Clarke was ruled out after the first cricket Test against India in December with an serious hamstring injury, and in his place Steven Smith had filled in as the Australia captain.
Meanwhile, Lehmann has issued a warning to out-of-form Australia vice-captain George Bailey, saying he needs to score runs to assure his place in the final XI during the World Cup.
"He knows that better than most. As selectors, we'll sit down and work out what the best side is and what the best combo is when they're all fit and available.
"George like everyone else will have to play well to play in the final 11. There is no difference between the top player and the 15th player. We are a squad and one thing I know about World Cups is that you need a squad to win it," he added.
In Clarke's absence Bailey is expected to lead Australia in their World Cup opener against rivals England at the Melbourne Cricket Ground on February 14.