Doctors said the 39-year-old senator had "barely" responded to medical interventions that included brain surgery following the assassination attempt.
Uribe was shot on Saturday as he addressed a small crowd of people who had gathered in a park in Bogota's Modelia neighbourhood.
On Sunday hundreds of people gathered outside the hospital where Uribe is being treated to pray for his recovery. Some carried rosaries in their hands, while others chanted slogans against President Gustavo Petro.
Petro has condemned the attack and urged his opponents to not use it for political ends. But some Colombians have also asked the president to tone down his rhetoric against opposition leaders.
The assassination attempt stunned the nation, with many politicians describing it as the latest sign of how security has deteriorated in Colombia, where the government is struggling to control violence in rural and urban areas, despite a 2016 peace deal with the nation's largest rebel group.
The attack on Uribe comes amid growing animosity between Petro and the Senate over blocked reforms to the nation's labour laws.
Petro has delivered fiery speeches referring to opposition leaders as "oligarchs" and "enemies of the people."
The Senate was expected to vote this week on the labour legislation that Colombia's president wants to enact through a referendum.
In a joint statement nine opposition parties said they will turn to "international entities" that can provide them with "conditions of equality that have been denied" to them by Colombia's government.
The Attorney General's office said a 15-year-old boy was arrested at the scene of the attack against Uribe.
The suspect was injured in the leg and was recovering at another clinic, authorities said.
On Monday, Colombia's Attorney General Luz Adriana Camargo said minors face sentences of up to eight years in detention for committing murders.
She acknowledged that lenient sentences have encouraged armed groups to recruit minors to commit crimes, but said Colombian law also considers such minors as victims, and is trying to protect them.
Camargo said officials had not identified any death threats against Uribe prior to Saturday's assassination attempt. But on Monday, Uribe's lawyer said he has sued the director of the National Protection Unit, a government agency that assigns security guards and bullet proof vehicles to politicians and human rights leaders.
Uribe launched his presidential campaign in October. His lawyer, Victor Mosquera, said the National Protection Unit ignored multiple requests by Uribe to have his security detail expanded as he campaigned.
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