"The coalition is talking a lot again. We could see some allies want to volunteer troops," Esper said.
According to the agency, the defence secretary gave no indication that a new contribution was imminent.
"If an allied country, a NATO country, decided to give us 50 people, I might be able to turn off 50 people," Esper added in the interview, which was taken on Tuesday on his flight back from the NATO summit in London.
Esper stressed that US troops in northeastern Syria have completed their manoeuvres as needed and that the total number of troops on the ground would remain around 600.
The movement of US forces in Syria has been a cause for much uncertainty in the region ever since US President Donald Trump abruptly announced a withdrawal of troops from the country in early October.
The fallout from the move included a Turkish operation against Kurdish forces it considers terrorists, a deal struck between Russia and Turkey to ensure a safe zone, and the return of Syrian government forces to the region for the first time in years.
The pullout was never completed, however, as US troops eventually set up camp at Syrian oilfields controlled by allied Kurds, claiming to ensure that resources were not taken by the Daesh* terrorist group.
Trump, while at the NATO Summit earlier this week, credited US forces with protecting oil from falling back into the hands of terrorists.
*Daesh (also known as IS/ISIS/ISIL/Islamic State) is a terrorist group banned in Russia
