The 23-year-old has emerged as an attractive option for the French club.
According to Sky Sports Deutschland, Marseille have already opened discussions with the German side over a potential transfer.
However, no agreement has been reached, while Bournemouth and Fulham are also reportedly interested in the United States international.
Scally, whose contract with Gladbach runs until 2027, is understood to be open to a move this summer.
The versatile defender came through the New York City FC academy before joining Gladbach in 2021 and quickly established himself as a regular.
He has made 167 appearances for the Bundesliga club, contributing five goals and nine assists. Scally has also earned 28 caps for the United States and featured twice at the 2022 World Cup.