Nepal said they were keen to select Lamichhane, who had his eight-year sentence for rape quashed on appeal last week.
Cricket Association of Nepal president Chatur Bahadur Chand told AFP on Thursday that they were "trying to see if we can still make it possible for him to join".
Former captain Lamichhane said late on Wednesday that the US Embassy in Nepal had "denied my visa for the T20 World Cup", calling the decision "unfortunate".
"I am sorry to all the well-wishers of Nepal Cricket," Lamichhane posted on social media platform X.
Lamichhane, 23, was once the poster boy for cricket in Nepal, but was not included in the original squad because of the conviction for raping a young woman in a Kathmandu hotel in 2022.
Nepal are making their second appearance in the T20 World Cup and will face the Netherlands in their opening match in Dallas on June 4, followed by group games against South Africa, Sri Lanka and Bangladesh.
Before his rape trial, Lamichhane's success as a leg-spinner had dramatically boosted the sport's profile in the Himalayan republic.
Lamichhane, speaking outside court after his acquittal on May 15, where he was greeted by cheering fans, said he would "try as much as possible to take Nepal much higher than I did before".
In 2022, when an arrest warrant was first issued, Lamichhane initially failed to return from Jamaica, where he was playing in the Caribbean Premier League.
He was dismissed as national captain and arrested, but Nepal lifted his playing ban when he was freed on bail.
It allowed him to keep playing, including at last year's Asia Cup in Pakistan and Sri Lanka, until he was convicted in January.
Cricket does not enjoy the same adulation in mountainous Nepal as it does elsewhere in South Asia.
But the sport has been growing in popularity, with Nepal given one-day international status by the world governing body in 2018.
Lamichhane was a major part of the rise as the most sought-after Nepali cricketer in lucrative T20 leagues around the world.
The leg-spinner's big break came when he was snapped up for the Indian Premier League, the world's richest cricket tournament, in 2018.
The World Cup will be played in the United States and the West Indies beginning on June 1.
