Lukaku revealed that he expects an update on his future next week as Inter try to prise the Belgium star from Old Trafford, where Marcus Rashford has become Ole Gunnar Solskjaer's first-choice striker.
Antonio Conte's Inter have made no secret of their interest in the 26-year-old, but the Serie A side's reported offer of €70 million (£63m/$79m) – comprising of a two-year loan and a €60m obligation to buy – has apparently fallen short of United's €83m (£75m/$94m) asking price.
Asked if he was optimistic about Lukaku following speculation Inter could turn to Eintracht Frankfurt's Ante Rebic, CEO Marotta told reporters: "Yes, I am optimistic about everything."
Lukaku was not included in the squad for United's 2-0 win over Perth Glory in their opening pre-season fixture in Australia on Saturday.
The ex-Everton striker – contracted to the Red Devils until 2022 with the option of a further year – joined United from the Toffees for £75m in 2017.
Lukaku, who has acknowledged a desire to play in Italy and hinted his future could be away from Manchester, scored 12 Premier League goals last season.
Juventus are weighing up a potential swoop for Icardi despite an already busy summer of signings for the Serie A champions.