The young Spanish forward was ruled out of action for seven weeks on Tuesday after suffering a second grade tear of the medial collateral ligament in his left knee in his first training session with the club.
Morata completed his move to the Italian champions from Real Madrid on Saturday but his injury leaves Juve with Carlos Tevez and Fernando Llorente as their only frontline strikers.
With the departure of Fabio Quagliarella to city rivals Torino, bringing in a new face is something Juve's chief executive is looking into, however he refused to comment on speculation linking Samuel Eto'o with a move to Juventus Stadium.
"I can confirm we are looking for another forward," Marotta said at a media conference for the signing of midfielder Roberto Pereyra.
"We've never talked about Eto'o. The squad needs at least five strikers, so we are missing someone, especially considering Alvaro Morata's injury.
"Whether the target is Eto'o or someone else, I prefer not to say.
"We are keeping a close eye on the evolution of the market, though obviously there are many problems with the clubs who own the players we are interested in.
"It changes hour by hour."
Marotta also reiterated Juve's determination to hang on to midfielder Arturo Vidal despite reported interest from Manchester United.
On Thursday the player rejected any talk of a move to the Premier League, and Marotta was quick to emphasise the club are not interested in seeing him leave.
"There is no reason for him (Vidal) to leave," he added. "It's very simple. Vidal extended his contract with us last season, as there was a reciprocal desire to continue this relationship.
"I can assure and confirm Vidal is happy to be with us and there's no reason for alarm."
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