It is understood that Sainz had a Richard Mille watch - the Alexander Zverev model named after the German tennis player worth £235,000 - taken as he left the Armani Hotel on Viale Manzoni.
Three people, who are thought to have been waiting outside the hotel for some time, encountered Sainz and stole his watch.
The F1 driver then set off in pursuit with his personal trainer, while bystanders who had seen the robbery also attempted to help intervene.
Sainz and his assistant managed to stop one of the three robbers after a car, then foot, chase.
The second robber was then stopped on Via della Spiga by Sainz’s manager.
The third was stopped very shortly after with the help of another one of Sainz’s personnel.
Police officers then arrived on the scene and took the robbers, aged between 18 and 20, into custody.
Sainz retrieved the Ferrari team sponsor watch before returning to his hotel.
Sainz posted on social media: "As many of you already know, yesterday we experienced an unfortunate incident in Milano. The most important thing is that we are all OK and this will only remain as an unpleasant anecdote.
"Many thanks to all the people who helped us yesterday, to the Milan police for their quick intervention and thanks for all your messages."
Last year, Sainz’s Ferrari team-mate Charles Leclerc was also victim of a robbery in the week leading up to the Emilia Romagna GP in Italy.
Leclerc’s Richard Mille watch (of similar value to Sainz’s) was taken from his left wrist as he stopped for photographs in the Tuscan city of Viareggio.
Then leading the drivers’ championship over Max Verstappen, Leclerc was with his friends and trainer Andrea Ferrari as a large crowd formed. Leclerc chased after the thieves and local police launched an investigation into the incident.
Trainer Ferrari called out the lack of street lighting. He posted on social media at the time: “Via Salvatori has been completely in the dark for months. We have been reporting this for months.
"Well, yesterday evening in Via Salvatori, they have robbed us. Think of arranging the lamps sooner or later? Asking for a friend."
Swiss watch maker Richard Mille is a long-time sponsor of Leclerc and became an official partner of Ferrari in 2021.
That year, McLaren racer Lando Norris had a prototype Richard Mille snatched from his wrist after the final of the Euro 2020 at Wembley Stadium.
