Kubiak and Manziel both are former Texas A&M quarterbacks. But before the Broncos would make any move on Manziel, the sources said, the Broncos want to see how his pending legal issues and potential NFL discipline are resolved.
The Dallas police department referred a domestic violence case against Manziel to a grand jury in late February. The grand jury was to consider whether to charge the former Cleveland Browns quarterback on allegations that he attacked his ex-girlfriend. But the grand jury ended its term last week without hearing the misdemeanor assault case against Manziel, the Dallas County District Attorney's Office recently told KTVT.
A new grand jury is expected to be seated within a week to 10 days. A misdemeanor assault charge carries a maximum punishment of one year in jail and a $4,000 fine.
Regardless of whether he is charged, the NFL is expected to discipline Manziel, and a suspension is considered likely, according to the sources.
Should the Broncos sign Manziel -- and that could be weeks or months away -- Denver, according to the sources, would do so with stipulations that would include mandatory counseling and possible clinical work for Manziel.
Manziel has been living in Los Angeles, and there are those, according to the sources, who are concerned about how he's faring there and in general. The Broncos would want to protect themselves knowing Manziel's history. Manziel had a 10-week stay in a rehab facility in Pennsylvania for undisclosed reasons starting in January of 2015.
On Thursday morning at the annual Boy Scouts of America breakfast at the downtown Pepsi Center where Kubiak was the keynote speaker, he said the Broncos are focused on the two quarterbacks currently on the roster.
The Broncos also have had trade discussions with the San Francisco 49ers regarding Colin Kaepernick but would need the quarterback to agree to a pay cut from his scheduled $11.9 million salary for 2016, a sticking point that has stalled talks. Denver also is expected to take a long look at the quarterbacks in the draft.
ESPN's Jeff Legwold contributed to this report.