The 27-year-old Troicki was suspended for 18 months by the International Tennis Federation (ITF) in July for not providing a blood sample at the Monte Carlo Masters in April.
The ban, which runs until January 24, 2015, means he will miss Serbia's Davis Cup semi-final against Canada in Belgrade next month and the opportunity of a second Davis Cup title.
Troicki's defining career moment came when he clinched Serbia's first Davis Cup in an emotional fifth rubber in the 2010 final against France in Belgrade, after which he and Djokovic were lauded in the Balkan state.
"We're not sure what's going to happen with Viktor," Djokovic said after his opening win at the Rogers Cup in Montreal before adding he doubted Troicki would be eligible for the Davis Cup tie.
"We all give him big support because he's definitely innocent ... Hopefully he is going to be able to be on the court very soon."
Troicki has denied any wrongdoing and said because he was not feeling well the doping officer had told him he could skip the blood test. Troicki had already given a urine sample.
The ITF dismissed his reasons for failing to provide the sample as 'not compelling' and he said he would appeal to the Court of Arbitration for Sports (CAS).
(Editing by Greg Stutchbury)
