The Giants announced the deal around 4 p.m. Tuesday, the time teams needed to reach the NFL's 75-man roster limit.
Earlier in the day, the Giants had said that they were waiving McManus, who battled incumbent Josh Brown for the starting job.
However, the strong-legged McManus was traded later to the Broncos, who are in need of a kicker after Matt Prater was suspended for the first four games for violating the NFL's substance-abuse policy by drinking beer. He has been in the league's drug program, which includes alcohol, since a DUI arrest on Aug. 12, 2011.
McManus had made both of his field-goal attempts - from 47 and 46 yards - and both of his PAT tries in the preseason. He is second in the NFL this preseason with 10 touchbacks. McManus, who was in the Colts' training camp last year, scored a school-record 338 points at Temple.
''He's one of those guys that's going to be a lifer,'' Josh Brown said of McManus. ''He's going to be a 10-year guy, easily. He's got that kind of talent and he's got that kind of head on his shoulders.
''So yeah, it does make me feel good to be 12 years in and to be able to continue to produce consistently on a daily basis and he's going to latch on somewhere and sink his feet in. He's going to be good.''
In getting down to the 75-man limit, the Giants also placed safety Cooper Taylor and receiver Marcus Harris on injured reserve. Taylor hurt his left foot in Indianapolis on Aug. 16. Harris sustained a hip injury against the Jets on Friday night.
The team also waived 13 other players, two with injuries - linebacker Justin Anderson (hamstring) and defensive end Emmanuel Dieke (knee).
Also released were cornerbacks Charles James and Ross Weaver; safeties C.J. Barnett and Kyle Sebetic; linebacker Spencer Adkins; wide receiver Travis Harvey; tight ends Xavier Grimble and Jerome Cunningham; guard John Sullen and defensive tackle Everett Dawkins.
Taylor and James were the only players among the 15 who played for the 2013 Giants. Adkins and Dawkins were the only other players with NFL regular-season experience.
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