Raiders second-round draft pick Obi Melifonwu answers questions from the media during rookie minicamp on Friday, May 5, 2017, at Oakland Raiders Headquarters, in Alameda, Calif. Benjamin Hager Las Vegas Review-Journal @benjaminhphoto

ALAMEDA, Calif. — The Raiders lost their second-round pick to a second surgery in four months.

Rookie safety Obi Melifonwu was placed Friday on injured reserve for the second time this year. He underwent an arthroscopic knee procedure in late August, forcing him to miss the first eight games before being activated onto the 53-man roster.

His season is over for good following a Thursday hip surgery, coach Jack Del Rio said Friday. This is the latest chapter to a difficult year for the defensive back and team’s rookie class.

Melifonwu played 34 defensive snaps in 2017. Seven came during his Nov. 5 season debut against the Miami Dolphins. Amid season-long struggles at left cornerback, the Raiders made a surprising move following the ensuing bye week to start Melifonwu at the position against the New England Patriots in Mexico City.

It didn’t seem a fair assignment in which to ask him to succeed.

The 23-year-old exited in the first quarter because of breathing difficulties at the high-altitude Estadio Azteca. He returned but struggled, being pulled early in the third quarter after a deep 64-yard touchdown from quarterback Tom Brady to wide receiver Brandin Cooks.

The Raiders fired defensive coordinator Ken Norton, Jr. two days later. Melifonwu played one defensive snap during the next three games. His focus now is recovery.

He joins cornerback Gareon Conley, the team’s first-round pick, on injured reserve. Conley was first sidelined in mid-June to a shin ailment. Rest and time proved ineffective remedies. He missed training camp, the preseason and Week 1 before playing in Weeks 2 and 3. The ailment still wasn’t right. Ultimately, he had surgery on Nov. 20.

Conley finished 2017 with 92 defensive snaps, putting the combined total for the Raiders’ top two picks at 126.

Aside from special teams, third-round defensive tackle Eddie Vanderdoes has played 383 snaps this season. Fourth-round offensive tackle David Sharpe (three), fifth-round linebacker Marquel Lee (127) and four seventh-round choices — safety Shalom Luani (86), offensive tackle Jylan Ware (zero), running back Elijah Hood (zero) and defensive tackle Treyvon Hester (331) — round out the group.

Luani ranks second on the team with 242 reps on special teams.

Nicholas Morrow leads all Raiders rookies with 573 snaps, including 420 on defense. He went undrafted out of Greenville College, a Div. III school in Illinois.

And so, this largely amounts to a redshirt year for Melifonwu, who missed a good chunk of training camp, too, with an ankle injury. The Raiders had high hopes for him this offseason, hoping he’d be contribute immediately in their sub-packages, specifically to shadow an opponent’s top receiving tight end. Aside from brief work in Miami, the role never came to fruition.

Cornerback Antonio Hamilton (knee) was activated from IR to assume Melifonwu’s roster spot.

Hamilton said that he learned during Friday’s practice he’ll play Sunday against the Dallas Cowboys. He has missed the past eight games.

More Raiders: Follow all of our Raiders coverage online at reviewjournal.com/Raiders and @NFLinVegas on Twitter.

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