Raiders’ Darren Waller OK after suffering shoulder injury

NAPA, Calif. — The Raiders received an injury scare Friday with their starting tight end.

Darren Waller exited late into a morning practice, walking off the field with athletic trainers. He suffered a shoulder injury that is not expected to sideline him for a prolonged period, two people familiar with the matter said. The official diagnosis was an AC joint sprain.

A situation involving backup guard Denver Kirkland, who was carted off the field as practice concluded, also looked worse to onlookers than it was. He was dealing with muscle cramps.

Losing Waller would have been a significant blow to the Raiders, who are giving the converted wide receiver a chance to see extensive playing time after Jared Cook’s March departure in free agency. Waller, signed off the Baltimore Ravens’ practice squad in November, has exhibited big-play ability in limited action.

He seeks consistency in camp as he prepares for a career-high workload. Improving on some of the position’s finer details, such as coverage recognition, has been a focal point. Position coach Frank Smith has mentored the 6-foot-6-inch target to that effect.

Snaps are invaluable for Waller’s continued development.

He should start seeing them again soon.

Waller became the second tight end in two practices to make an early exit. Paul Butler, a reserve hoping to push for a 53-man roster spot, suffered a hip injury Thursday. The ailment is believed to be minor, and he could return this weekend.

Kirkland has seen work at second-team right guard with Jonathan Cooper busy on the left side.

Cooper is expected to start Weeks 1 and 2, since Richie Incognito is suspended and Denzelle Good is still recovering from lower back surgery. Through the first week of camp, Incognito has worked exclusively at first-team left guard. The Raiders’ plan is to elevate Cooper relatively soon so he can build chemistry with left tackle Kolton Miller and center Rodney Hudson.

The team will open its season Sept. 9 against the Denver Broncos.

Notable

■ Undrafted rookie fullback Alec Ingold might be seizing his opportunity as veteran fullback Keith Smith (knee) recovers from July meniscus surgery. “We had a great blitz period (Thursday),” coach Jon Gruden said. “Alec Ingold from Wisconsin has really done an excellent job as a lead back and a pass protector.”

■ Wide receiver Antonio Brown missed his second straight practice. He has missed five of six because of an apparent foot issue. He appeared in pads Tuesday but did not complete the session. “I think we’re all disappointed,” Gruden said. “We think he’s disappointed. We’d like to get the party started. We’d like to get him out here. He’s a big part of this team, but in the time being, we’re going to continue to work hard. We’ve seen the development of some other receivers we are excited about.”

■ Wide receiver Keelan Doss arguably had the catch of camp Friday … for about 10 minutes. During a 7-on-7, Doss sprinted past nickel back Lamarcus Joyner and made a full-extension dive to haul in a deep Mike Glennon pass. Less than 10 minutes later, Raiders season-ticket holders celebrated wide receiver J.J. Nelson, who used one hand to tip and control a deep Nathan Peterman throw while falling to the ground. Both plays were to the left sideline.

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Contact reporter Michael Gehlken at mgehlken@reviewjournal.com. Follow @GehlkenNFL on Twitter.