Orton was injured in the final minute of the first half in Sunday's 27-23 victory over the Detroit Lions, forcing the Bears to turn to former starter Rex Grossman. A source told ESPN's Michael Smith that a high ankle sprain will sideline Orton for at least a month.
"I'm not playing doctor; you shouldn't either," coach Lovie Smith said Monday. "You should let us come and tell you once we know for sure exactly what the injury is. We're hopeful, I'll just say that."
Orton was examined after the game and underwent tests Monday morning, Smith said. More were scheduled for later in the day, but the odds of him being ready for this week's game against the Tennessee Titans certainly did not look good after he went down against the Lions.
Asked if the injury was more than just a sprain, Smith said: "It's an ankle injury. That's about all I'm going to tell you right now. Wednesday, I'll tell you more."
He also offered few details about safety Mike Brown's calf injury, although Smith did say he doesn't think it's season-ending.
Smith said the Bears have no plans to bring in another quarterback.
"To do that, you would say that Kyle will be out for a long period of time," Smith said. "We're not there. We're evaluating an ankle injury. That's about all we're doing right now."
Team spokesman Scott Hagel said Monday night: "The evaluation process is ongoing and it will go through tomorrow."
Orton's agent, David Dunn, did not return a call seeking comment.
Orton was enjoying a breakout year after beating Grossman in a preseason competition before the injury in the closing minute of the first half. That happened moments after the Bears lost Brown, their emotional leader.
Brown walked to the locker room after Detroit's Jason Hanson booted a 52-yard field goal that extended Detroit's lead to 10 with 1:05 left.
Orton got up and took a few steps before crumpling to the ground. He was tended to for several minutes before being carted off the field. He was 8-of-14 for 108 yards and was in line for his sixth straight game with 199 yards or more.
Now, the Bears might be without him for a while.
"I don't want to be prepared for that," tight end Desmond Clark said. "Hopefully, he comes back and misses a minimum amount of time. At this point, I'm going to hold out hope that he's not going to miss much time because he was playing at an elite level, and hopefully, we can get him back as soon as possible."
Orton has 1,777 yards in all while completing 151 of 244 passes and has 10 touchdowns and four interceptions -- none in the past four games. He might not have been on his way to the Pro Bowl, but he was clearly playing at a much higher level than when he got thrust into the starting role as a rookie filling in for the injured Grossman in 2005.
Back then, Orton was simply a game manager. The Bears simplified their offense and limited him mainly to handoffs and short passes. And although Chicago went to the playoffs, fans couldn't wait for Grossman's return late that season.
On Sunday, they cringed when Orton went down. And they serenaded Grossman with boos, a familiar tune the past few seasons.
Although Grossman threw a 6-yard touchdown pass to Rashied Davis in the third quarter and scored the winning TD on a 1-yard sneak with 5:36 left in the game, he was erratic. There were deflections. There was an interception. And there were jeers before he gave the Bears the lead.
After he plunged into the end zone, Grossman ran to the right and slammed the ball to the ground.
Grossman's stats -- 9-for-19, 58 yards, one touchdown, one interception and a 49.9 rating -- were far from impressive. But the Bears have won with him in the past. He played at a Pro Bowl level early in 2006 before inconsistency set in. The Bears made the Super Bowl but fell to 7-9 last season, with Grossman getting benched for Brian Griese and then injuring his left knee late in the season.
That opened the door for Orton, leading to a quarterback competition.
"Rex has played a lot of downs around here," Smith said. "He's been in that position before."
Brown finds himself in a familiar spot, too: recuperating.
An Achilles tendon injury ended his season in 2004, and he missed the final four regular-season games the following year with a calf injury. In 2006, he started the first six games before going down with a foot injury, and last year, he tore the anterior cruciate ligament in his left knee in the opener at San Diego.
"It's a concern because it's happened so many times," Smith said. "But right now, he just has a calf injury. Mike doesn't have a season-ending injury."
Information from The Associated Press was used in this report.