ENGLEWOOD, Colo. -- Denver Broncos rookie quarterback Drew Lock said Thursday he isn't sure when he will be able to throw a football again, and coach Vic Fangio said it is possible Lock could at least open the season on injured reserve.

Lock suffered a severely sprained right thumb -- on his throwing hand -- early in the third quarter of Monday night's preseason loss to the visiting San Francisco 49ers. He underwent an MRI exam on Tuesday and a sprain was confirmed.

X-rays taken at the stadium Monday night were negative.

Lock will neither play nor practice for the remainder of the preseason, and he will be limited to conditioning work only.

"Obviously because it's his throwing hand and a thumb, that's a pretty serious injury for a quarterback,'' Fangio said. "It will be some time before we know exactly where he's at and how much time he would miss.''

"[I'm] trusting the [training] staff in there to get me back as soon as possible,'' Lock said. "Whenever that is, we'll decide on whenever I'm 100% ready to go.''

Lock, who was selected in the second round (42nd overall) of April's draft, was in a battle to be the team's backup quarterback behind Joe Flacco. Asked Thursday if putting Lock on injured reserve was now a possibility if his recovery time was slated to include part of the regular season, Fangio said: "Yeah, it could be if we don't think he can play for a while. The bad thing about it is because of the injury he can't do much.''

If Lock were to be placed on injured reserve with a designation to return, he would have to be on the Broncos' roster in Week 1 -- taking the spot of a healthy player at that time -- and have to miss half the season.

If he were to be placed simply on injured reserve, he would miss the entire season.

In the meantime, as the Broncos try to decide what to do based on his progress in healing, Lock has been in the quarterback meetings as well as on the practice field with the team. Because he cannot participate in drills, he said using the team's virtual reality system is going to be an important part of his recovery.

Lock said he will have to do "two times'' more classroom work since he will not be practicing, and "the VR stuff upstairs is going to be heavily used. ... It helps a lot, being able to see what Joe does, kind of from his angle and things ... being able to see every single rep, being able to see what the defense does, being able to see it in a ton of different looks.''

Lock said he used VR in his sophomore and junior years at Missouri, as well.

Lock played 30 snaps against the 49ers, finishing 7-of-12 passing with 40 yards to go with the sack he was injured on. Lock played just one more snap after that sack and left the game with just over 13 minutes remaining in the third quarter.

After opening training camp as the No. 3 quarterback behind Flacco and Kevin Hogan, Lock had been moved up to the No. 2 spot in practices, and he was the second quarterback into the game against the Seattle Seahawks and 49ers.

For the preseason, Lock has completed 60.8% of his passes with a touchdown and an interception.