Martinez continues to be linked with a move away from Serie A side Inter – LaLiga giants Madrid and Barca as well as Manchester United and Manchester City reportedly interested.
LaLiga holders Barca have been linked to Martinez as they eye a long-term replacement for veteran forward Luis Suarez.
Marotta was asked about Martinez prior to Sunday's 2-1 loss to Scudetto rivals Lazio in Rome.
"Lautaro is improving, he is a very young lad who I think is above all eager to wear this glorious jersey and grow professionally," Marotta told Sky Sport Italia.
"As I always say, players only leave Inter when they point towards that exit."
Martinez has taken centre stage alongside Romelu Lukaku since Mauro Icardi's initial loan move to French champions Paris Saint-Germain at the start of the season.
The 22-year-old has scored 16 goals across all competitions for Inter, who are third and three points behind leaders Juventus in Serie A.
Argentina international Martinez has netted 25 goals in total since arriving from Racing Club in 2018.