A league source confirmed Monday night that Dunbar will re-sign with the Rams on Tuesday morning.
The Rams released Dunbar on Sept. 3 as he was preparing to begin serving a four-game suspension for violation of the league's policy on performance-enhancing substances.
Dunbar was suspended Aug. 14. He dropped hints on Twitter on Monday night that he was going to return, posting a picture of his plane ticket from Miami back to St. Louis.
Should Dunbar's deal indeed amount to essentially what he had remaining on his original two-year deal, he'd make just shy of $1 million for the rest of the season. The Rams will have to make a corresponding roster move to create space for Dunbar.
Dunbar, who started all 16 games for the Rams in 2012, would have been eligible to return to the team's active roster this past Friday, one day after the team played San Francisco, had he not been released.
Since the Rams released him, they have to wait until the league completes all Week 4 games before he becomes eligible for reinstatement.
Dunbar finished second on the team in tackles in 2012 with 115 after signing with the Rams from New Orleans in the offseason. He added 4.5 sacks, 13 tackles for loss and a pair of interceptions.
Veteran Will Witherspoon, who stepped into Dunbar's spot in his absence, is dealing with a hamstring injury. Coach Jeff Fisher said when the suspension was announced that the team would re-evaluate the starting spot upon Dunbar's return. Given Witherspoon's injury, it appears the timing could work out for Dunbar to plug back into the lineup.