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That came out of nowhere. After facing the news of Kyle Juszczyk’s MCL sprain, the story of the day is how the 49ers were preparing without their jack-of-all trades fullback. Now, it’s Mike McGlinchey who will join Juszczyk on the sidelines for the next four-to-six weeks.

According to head coach Kyle Shanahan and the 49ers, McGlinchey will undergo arthoscopic surgery on his right knee. He said the injury occurred on one of two plays, but started on a play in which Deebo Samuel ran an end around in which McGlinchey made contact with Samuel and his defender and then got “rolled up on about a quarter later.” He came up limping, but stayed in the game initially, before Shanahan made the decision for him to come out.

“I think that’s why I wasn’t quite as worried about it when I talked to you guys Monday night,” Shanahan said. “He didn’t take himself out. He was limping a little bit, which he does a lot of games because they’re linemen and that does happen. As long as there’s no bad damage, then they’re usually alright. But he kept up with it, so I remember seeing him doing it, took him out personally, just telling me he didn’t want to go out because he didn’t think he was that hurt. He didn’t think he was that much after the game… He came in the next morning, was hurting a little bit more. When we checked it out, it was a surprise to him and surprise to all of us.”

The immediate replacement for McGlinchey is Daniel Brunskill, the 25-year-old tackle who the 49ers signed out of the American Alliance of Football with the San Diego Fleet. Veteran tackle Sam Young is the current swing tackle backup for Brunskill and left tackle Justin Skule

“I feel very similar to how I do about Skule,” Shanahan said. “I didn’t know much about him until he got here in OTAs and training camp. I got to see him then and I became a believe in him… He earned his spot on this team, did a real good job… Got in there for one play against Pittsburgh, did a hell of a job… Very similar to Skule in that the game’s not too big for him.”

With left tackle Joe Staley, who fractured his fibula against the Cincinnati Bengals in Week 2, expected to be return between Week 9 and Week 11, this leaves the 49ers without three of their key blockers for around the same period of time. Both Juszczyk and McGlinchey have timetables to return between Week 10 and 12.

There are also injured reserve candidates eligible to return around the same period of time, though none of them are offensive linemen. Kentavius Street (Week 9), Trent Taylor (Week 11), Jalen Hurd and Jason Verrett (both Week 13) are all eligible to return later in the season, though only two of the four can return.