The 21-year-old became Spurs' record signing when he joined for an initial fee of £25.7 million in August and is widely expected to be Gareth Bale's replacement - who joined Real Madrid in a world-record £86m deal.
And Sabatini says Lamela's move to White Hart Lane was in part influenced by Roma's desire not to strengthen an unnamed team in the same league.
|5/1||Erik Lamela is 6/5 with bet365 to score v Norwich
"Then some new factors came into play and as time went on we started to consider the eventuality. A club made him an offer that we didn’t and couldn’t match.
"Rather than trying to win a war that we probably wouldn’t, we opted to sell. When that Italian club offered him €3.5m [£2.9m] a season, as well as a €2m [£1.7m] commission to his agent father, we knew we had lost the player.
"His people started pushing for a renewal and that is when I started moves to sell him. Had we begun negotiations sooner then we probably could have sold him for an even bigger fee."
Roma also witnessed the big-money departures of Marquinhos and Pablo Osvaldo, to Paris Saint-Germain and Southampton respectively, but Sabatini denied they are a selling club and insists they remain competitive.
"No one obliged me to sell, but it was a tough market because it came after the Coppa Italia final loss," he added. "There was a compromised psychological dimension and we had to rebuild with what was left to us.
"However, the market was concluded satisfactorily and we are sure we have built a competitive team. We didn’t sell the future, we sold shreds of the future.
"We also signed players by spending important figures and there are still young players of value in the squad. Roma are not a selling club. We are working with the objective of being competitive."