"It's politics at play," Bobi Wine's lawyer Medard Ssegona told RFI.
"The regime is worried that being increasingly popular [he] is a threat to the sitting president [Yoweri Museveni]," he said.
Robert Kyagulanyi, known by his stage name of Bobi Wine, was one of five MPs arrested on 13 August in the north-western town of Arua.
The authorities accuse Kyagulanyi's supporters of throwing stones at Museveni's convoy and intimidating ruling party voters during the Arua Municipality bi-election.
The hotly contested race to replace slain MP Ibrahim Abiriga saw independent candidate Kassiano Wadri beat 11 others, including the ruling NRM candidate Nusura Tiperu.
Like several other independent candidates, Wadri had received the backing of Kyagulanyi, in a sign of the popstar-turned-politician's growing influence.
It's because of his popularity that the 35-year-old has been slapped with "trumped up charges" that include three accounts of unlawful possession of firearms and ammunition, reckons Ssegona.
"The hotel owner says no gun was ever found. A number of police officers are being forced to sign a certificate that they recovered a gun when they never participated in the arrest, the gun came from nowhere," he said.
Military vs. civilian court
For Ssegona, the charges are a pretext to charge Kyagulanyi in a military court, "which the president has full and absolute control over".
His family however, want him to be tried in a civilian court, insisting that he is in need of urgent medical care after being beaten up by security forces during his arrest.
"He suffered a lot of pain in the back, basically the left side he says is paralysed," Ssegona commented.
"He wants to get out as soon as possible because he's worried about his life. He might die in there. His testicles were squeezed by the military, so he suffers pain down there," he added.
But in a statement, Museveni said this was "fake news" and accused the young MP of forming "indisciplined groups".
"The more serious issue is these chronically indisciplined people attacking women and children” and “destroying people's property", the president was quoted saying in the state-run newspaper New Vision.
"Who is Bobi Wine or anybody to beat our people and for what?" Museveni challenged.
Not everyone is convinced by his argument. One of Tanzania's main opposition parties, ACT Wazalendo, has urged Museveni to free Bobi Wine under the #FreeBobiWine hashtag movement.
Meanwhile in Kenya, hundreds of people are expected to march to the Ugandan embassy in Nairobi on Wednesday to voice their anger over Kyagulanyi's detention, in echo of the protests that erupted in the Kampala capital on Monday.
Threat to Museveni, Besigye
"There is every ground for Museveni to get worried," reckons Innocent Ayo, Secretary for International Affairs with the Forum for Democratic Change (FDC), Uganda's main opposition party.
"The team which Bobi Wine did not have is seemingly taking shape," he told RFI.
"People who thought he was just some boy that was drinking cannot now stand, because now as we talk, there are credible leaders, including the likes of us that are within the opposition that are yearning for change," he said.
For Ayo, the popular MP is also a threat to the FDC's historical leader Kizza Besigye, following a divisive party election last year.
"As we talk, Besigye's popularity is reduced on its own, minus Bobi Wine. There are divisions in the party which have not been resolved," he explained, "so yes indeed Bobi Wine presents a formidable challenge to Doctor Kizza Besigye, because he can now lead the ones that could not be led by [Besigye]."
The same goes for disgruntled NRM MPs. Before, "they could not join the FDC because of Besigye's approach, now the NRM can easily find a home within the opposition alliance that is now rallying around Bobi Wine," he added.
"A young man has come and his message is appealing," particularly for young Ugandans, who he reckoned make up 70 percent of the population.
"Remember, he is a musician and he brings on board the youth and civil society that had not been voting FDC," Ayo commented.
The challenge now for Kyagulanyi--who is still an independent MP--is to build up a political team and a structure if he's to stand any chance of competing against Museveni in the 2021 presidential election, which he's hinted at contesting.
Yet even before getting that far, he first needs to win his legal battle, which resumes on Thursday when he returns to court.
"We are working around the clock to secure his release," Ssegona said, adding they hope to transfer his case to a civilian court that's "not biased, as soon as possible".
*No government official responded to RFI's interview request.