Thomas' recovery will take at least six months and, depending on the severity of the injury, he could miss all of next season.
"Heading to surgery this morning.. everyone keep me in prAyers that it goes well," Thomas tweeted Monday morning.
Earlier, he tweeted about his mother and grandmother, who have been incarcerated on drug charges since he was 12: "Only if i had my mother and granny here with me, stuff would be so different."
Thomas had a tough year after leaving Georgia Tech following his junior season.
He fractured his left foot in pre-draft workouts but was still the first receiver selected in the draft when the Broncos chose him at No. 22, three spots ahead of their other first-round pick, quarterback Tim Tebow.
Thomas was just starting to flash his athleticism and mobility, using his 6-foot-3, 230-pound frame to outjump defenders when he re-injured his surgically repaired foot early in training camp and didn't return until after the opener.
He had a spectacular debut in Week 2, catching eight passes for 97 yards and a touchdown against Seattle, but he never tallied more than three catches in any game the rest of the season. He was knocked out of one game with a concussion while returning a kickoff and was also sidelined for the final five weeks of the season with a sprained ankle.
Thomas played in 10 games, starting twice and finishing with 22 receptions for 283 yards and two scores. He also returned 16 kicks for a 24.9-yard average.
He showed enough promise, as did fellow rookie Eric Decker, for new coach John Fox to proclaim upon his hiring that the wide receiver corps led by Pro Bowler Brandon Lloyd and Jabar Gaffney was the area that needed the least attention during the team's massive makeover.
First, slot receiver Eddie Royal underwent a hip operation that will keep him out at least until late May, and now Thomas will be sidelined at least through August and maybe much longer.
Royal's surgery briefly opened a window for Thomas to get more playing time, but he got hurt Wednesday while working out in Atlanta, where he lives in the offseason.
The Broncos might now have to consider drafting a wide receiver in April.