The 64-year-old head of the EU's executive is at the end of his five-year mandate and is expected to hand over the reins to Ursula von der Leyen, Germany's former defence minister, at the end of next week.
His November 11 surgery, to treat an aortic aneurysm in his abdomen, and subsequent convalescence in a German hospital meant he was unable to appear as a witness in a Luxembourg trial dealing with a case back from 2007 when Juncker was Luxembourg's premier.
The trial was meant to be held in November 2017 but was delayed because of Juncker's packed agenda as Brussels' top EU official.
Twelve hearings had been set aside for the case, in which three agents of Luxembourg's SREL intelligence agency are accused of using illegal wiretaps.
Fall-out from that scandal triggered an election that saw Juncker pushed from power after 18 years at Luxembourg's helm.
Von der Leyen is expected to become the new European Commission president from December 1.
EU ambassadors in Brussels were holding a meeting Friday to approve the list of her commissioners.
That team has been drawn from all EU member states -- except Brexit-bound Britain, which has refused to nominate a commissioner because it is in a campaign period leading up to December 12 elections.
The European Commission has started legal action against London for breaching that obligation.
Britain has a final deadline of midnight Friday (2300 GMT) to offer up a name, but is considered unlikely to do so.
With Britain scheduled to leave the EU at the end of January, the Commission's move is a legal gambit to head off any future challenge to decisions made without a full roster of commissioners from all current member states.