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San Francisco 49ers cornerback Richard Sherman, who injured his hamstring during Friday's practice, is expected to miss the Niners' preseason opener against the Dallas Cowboys this upcoming Thursday.

The San Francisco 49ers will be without their No. 1 cornerback, Richard Sherman, when they take on the Dallas Cowboys at Levi's Stadium this Thursday for both teams' 2018 preseason opener.

Sherman injured his hamstring during training camp practice last Friday while covering wide receiver Pierre Garçon. Sherman came up limping a bit, and the Niners held him out of the rest of camp. The three-time first-team All-Pro sat out of practices Sunday, and the Niners revealed the injury was a little worse than initially thought.

"At least a week," head coach Kyle Shanahan told reporters in regards to Sherman being out. "We're definitely going to rest him at least a week. We don't think it's going to be anything long term. It's Grade 1, a little higher than we expected, so we've got to be careful with that."

The 49ers have been easing Sherman back into practice after he was cleared from his 2017 Achilles injury just before training camp. A week ago, defensive coordinator Robert Saleh noted the veteran corner was still working on "getting his football legs back."

"He doesn't have anything to prove," Saleh said of Sherman on July 29. "He has to just get back in shape and get his legs back."

This latest injury will hinder that progress, although the Niners have little reason to rush Sherman back into the fray. What it does mean, however, is getting fellow cornerback Jimmie Ward (hamstring) back into full practice will be pretty important. And it also opens up more opportunities for depth corners, including rookies Tarvarius Moore and Tarvarus McFadden.

McFadden had an interception off a deflected pass in practice Sunday.

Cornerback depth was one of the bigger concerns the 49ers had entering 2018. Aside from Sherman, the Niners may see nickel cornerback K'Waun Williams out for a length of time, as he appeared to roll his ankle during practice. This will likely translate into more reps for first-year nickel D.J. Reed between now and Thursday.

San Francisco has two more days of camp practice this week before a walk-through on Wednesday. The 49ers then open up their 2018 preseason against the Cowboys, kicking off at 10 p.m. ET on Thursday.

Peter Panacy has been writing about the 49ers since 2011 for outlets like Bleacher Report, Niner Noise, 49ers Webzone, and is occasionally heard as a guest on San Francisco's 95.7 FM The Game. Feel free to follow him, or direct any inquiries to @PeterPanacy on Twitter.