Guzan left MLS for England in 2008 to sign for Aston Villa, where he played until making the switch to Boro this summer. But the Premier League club have started Victor Valdes over Guzan since September.
That has led Guzan to explore a move back to the U.S., according to the report, which cited a source as saying the 32-year-old is "testing interest" from MLS clubs.
Guzan is from the Chicago area, and while the Fire currently hold the top spot in the MLS allocation order, expansion club Atlanta United -- followed by Minnesota United -- will move above them before the goalkeeper can become available in the January transfer window.
Both expansion clubs could use a goalkeeper of Guzan's stature -- and reportedly have the allocation money to sign him -- so Chicago would need work a trade with Atlanta to return to the top slot.
And such a move could already be in the works, as the official MLS website reported that Atlanta is close to a deal to acquire goalkeeperSean Johnson -- a Georgia native -- from the Fire.
Any deal could happen when the MLS trade window opens temporarily on Dec. 11, the league said.
Johnson started for Chicago from 2011-15 and after the losing the starting job to Matt Lampson at the start of this season, won it again and made 22 starts.
Atlanta already has young goalkeeper Alexander Tambakis, whom the club signed as its first-ever player in January.
If Guzan returns to MLS, where he previously played for the now defunct Chivas USA, he would follow on the heels of fellow U.S. keeper Tim Howard, who moved to the Colorado Rapids this summer after a long tenure in England.