"For this week, yes," Fox said.
Tebow said he doesn't feel as though he's on a week-to-week basis but that he's not one to fret about the future anyway.
"It's just take it one day at a time, consistently trying to get better and not focusing too far in the future," Tebow said. "Today's the day I've got to improve, and that's kind of the focus."
By not committing to him beyond Sunday's game at Oakland, Fox made it clear that Tebow has to quickly improve as a pocket passer to retain his starting status in Denver.
"I think at the end of the day, we've got to see if he can improve and get better in the passing game," Fox said.
Since supplanting Kyle Orton at halftime against the San Diego Chargers on Oct. 9, Tebow has completed 46 percent of his passes (35 for 76) and been sacked 13 times. His passer rating this season is 75.1, almost identical to the 75.7 rating that cost Orton his starting job during the team's 1-4 start.
Tebow, who pulled out a stunning win at Miami two weeks ago in his first start this season despite playing poorly for most of the game, said he feels as though the coaching staff still has his back.
"I think they have confidence in me, but more than anything, I've got to have confidence in myself and my teammates around me and at the end of the day that's what matters," Tebow said.
"You know, really, in this business all things are possible," Fox said. "And Brady's a guy that we acquired before I got here, but he's shown flashes in our practice and (preseason) games, so right now we're in the process of finding out who the quarterback is and we'll leave it at that."
Notes: Broncos RB Willis McGahee said he'll test his surgically repaired right hand this week in hopes he can return to action after missing Sunday's game. He was hurt at Miami two weeks ago when his right hand got stuck in a defender's face mask, drawing an infraction that cost him a $7,500 fine, which he said he's appealing.
The Associated Press contributed to this report.