Welker, who suffered a concussion just before halftime of the Broncos' victory over the Tennessee Titans on Dec. 8, was held out of Thursday night's loss to the San Diego Chargers. Welker also suffered a concussion in the Broncos' Nov. 17 win over the Kansas City Chiefs.
Before he can play in a game, Welker would have to be declared symptom-free by both the Broncos' medical staff and a designated independent physician who has been approved by the NFL and the players' association. Welker would then have to proceed through multiple days of limited activity before he could return to practice on a limited basis.
Andre Caldwell, who got most of the snaps last week in Welker's absence, is expected to be the team's third receiver Sunday against the Houston Texans. Caldwell had six catches for 59 yards and two touchdowns against the Chargers.
"I thought Bubba Caldwell played really well," quarterback Peyton Manning said. " ... Great route on that first touchdown, did a great job getting in the end zone on a play he hasn't [worked] that much, so that's a good job knowing what to do, being in his playbook. We'll count on him this week if he has to play."
Asked after practice to gauge Welker's recovery to this point, Fox said, "I just know he's not cleared to participate yet, and he'll be day-to-day moving forward."
Cornerback Kayvon Webster, who had surgery Friday to repair a fractured right thumb, also was held out of Wednesday's practice. Webster will miss Sunday's game but is expected to be able to play using a cast on his surgically repaired thumb in the regular-season finale against the Oakland Raiders.
Champ Bailey, who has played in just three games this season because of a left foot injury, is expected to be in the lineup against the Texans and took part fully in Wednesday's practice.
Defensive end Derek Wolfe also continues to be held out of practice and is working with the team's strength and conditioning staff. However, the Broncos showed at least some optimism about Wolfe's potential return when they kept him on the roster after signing former Jacksonville Jaguars defensive end Jeremy Mincey on Tuesday.
To make room for Mincey, the Broncos released center J.D. Walton.