The Bears set a number of franchise records on offense last season, including most total yards (6,109), most passing yards (4,450), most passing touchdowns (32) and most first downs (344).
Marshall hailed the offence as a "special group" of players but insists that they need to prove themselves yet again next season.
"I think we have a special group. We work hard. Their approach to practice to their approach to the film room, it's amazing, and I think if we continue to do that, we'll continue to grow," Marshall is quoted as saying by ESPN.
"We have a tremendous upside, but again, we have to prove it. What we did last year was really tough. You bring in a new coach with a really sophisticated offense. You've got [quarterback] Jay [Cutler], he's been in different offenses almost every other year. It's tough transition.
"So for us to make that big of leap last year says a lot about our coaching staff and our players. This year, I think that's something to build off, and we can possibly even be better."
While Chicago's offense was impressive last season, their poor defensive showings ensured that they missed out on the playoffs and ended the campaign with an 8-8 record.