Manning, who wore a brace on his ailing right ankle in Sunday night's win over the Kansas City Chiefs, sat out practice Wednesday, though he did participate in the Broncos' walk-through earlier in the day.
He is expected to practice through the remainder of the week.
"You always like to be out there," Manning said. "Just kind of following [head trainer Steve Antonopulos'] and the doctors' orders."
Wide receiver Wes Welker is working under the guidelines of the league's concussion protocol, which meant despite passing a baseline cognitive exam Monday, he was held out of practice Wednesday. Under the protocol he can participate in the "non-contact'' parts of practice Thursday and could take part in the full practice Friday.
"He's working through the protocol and they're increasing activity as he clears hurdles and all that," interim coach Jack Del Rio said. "And when they give him the green light, we'll get him out there."
Welker suffered a concussion after a 20-yard catch-and-run play in Sunday's win. He initially left the game, returned for four plays and made one more catch, then was pulled from the rest of the game.
If Welker participates in Thursday's practice on a limited basis, he likely would be on track to play Sunday at New England.
Dreessen has routinely been held out of Wednesday practices since having two knee procedures done in the offseason. Thomas suffered his injury late in the third quarter.
Cornerback Champ Bailey (left foot) practiced on a limited basis.