The Chile forward underwent surgery in midweek after his injuring his left ankle on international duty.
Sanchez, 30, could be out for up to three months but Marotta believes Antonio Conte's squad is deep enough to handle his absence.
Inter did not miss the Manchester United misfit in Monday's (AEDT) thrilling 4-3 victory over Sassuolo, secured courtesy of braces from Romelu Lukaku and Lautaro Martinez.
"The January market is available to the club but the strongest players aren't available for moves in that window," Marotta said.
"We'll be alert to examine any potential opportunities. We have a competitive squad. Obviously we'd be happier without the Sanchez injury but we're optimistic.
"When Alexis comes back the attacking set-up will remain unchanged."
Lukaku and Martinez starred as Inter ran riot for over 70 minutes at Mapei Stadium.
The visitors were three goals clear and cruising before Filip Djuricic poked in Sassuolo's second goal in the 74th minute.
Fellow substitute Jeremie Boga reduced the margin back to one and the Nerazzurri had to survive a nervy finish to secure their seventh win in eight Serie A matches.
Antonio Conte battled a fever before the game and left it to his assistant, Cristian Stellini, to explain the "blackout" that put three points in jeopardy.
"We lost the ball twice and they caught us by surprise when breaking quickly," he said.
"It was too easy for them to score. We've still got a long way to go and working on situations like this is the most important thing for us."
Stellini said: "Antonio is slightly worn out, he had a bit of a fever before the match. He gave his all so he could lead the team, as he always does over the course of the 90 minutes.
"Thankfully he wasn't kept away from the bench but he's feeling the effects again now."
Stellini said Stefano Sensi, who missed the match with a thigh injury, would be assessed on Monday ahead of the Champions League game against Borussia Dortmund.