The Italian is now facing a lifetime ban after the the International Cycling Union (UCI) announced the 30-year-old had tested positive for testosterone on 22 October.
Santambrogio was serving an 18-month ban, which expired 2 November, for using the blood-booster EPO while riding for Italian team Vini Fantini at the 2013 Giro d'Italia.
He was stripped of his Stage 14 victory and disqualified from the race where he had finished in 9th place on the general classification.
Santambrogio received a reduced 18-month ban this year after giving evidence to the UCI's Independent Reform Commission.
That evidence and seeming contrition earned him a second chance in cycling, and he recently signed a two year contract with Ukrainian registered continental team Amore & Vita.
Now provisionally suspended, he has the right to request and attend the analysis of the B sample.