The Bears fell to their fourth defeat of the season, and lost their third game in a row at home, as the Miami Dolphins claimed a 27-14 victory at Soldier Field.
When asked about those reports, Marshall told reporters: "OK, were you in here? Were you in this locker room? This is a team matter. That has nothing to do with you. There's a lot of guys this means a lot to.
"We're 3-4. We need to play better. That's unacceptable. That's unacceptable. Unacceptable; shouldn't have lost today, shouldn't be 3-4. [The] offense [has] got to play better. It's as simple as that."
The Bears are 3-4 in their campaign and face the New England Patriots next week.