OAKLAND, Calif. -- From a 3-for-4 game to the intensive-care unit. It was that kind of a Friday for Neil Walker.

"First night ever in San Francisco turns into a nice baseball night for myself," the Pirates' second baseman said Saturday in the Oakland-Alameda County Coliseum visitors' clubhouse, barely 19 hours after sustaining what he called a mild concussion in a collision with outfielder Ryan Church.

"Then ... to end up in the hospital, I don't think that's a good night at all."

Walker sat out the game Saturday night against the A's and will do the same today. After taking the team charter to Chicago tonight, he is scheduled to return to Pittsburgh late Monday morning for follow-up examinations by the Pirates' team doctors and more.

He aims to rejoin the club before it concludes its Cubs series Wednesday at Wrigley Field. But the Pirates and manager John Russell want to take no chances because Walker lost consciousness for a minute or so after chasing a foul popup behind first base and collided, back of his head to Church's right knee, to start a seven-run A's seventh inning in a 14-4 Oakland victory.

"It's a sting," Russell said of temporarily losing Walker, who had a double, single and homer before the injury and is batting .295 with three homers and 12 RBIs.

"We'll miss him. Neil's obviously been doing a very good job. But you don't want to mess around with something like this."

Suffering from a headache and sleep deprivation due to hourly checks at Alta Bates Summit Medical Center, Walker showed up late Saturday afternoon in the Pirates' clubhouse after a couple of hours of sleep at the team hotel and declared himself fortunate and fine.

"However long it was between I got hit until when the trainers came out, I was out cold," he said. "I don't remember getting hit. I just remember waking up and seeing their team doctor [from the Oakland Athletics] in front of me.

"When I got up, I felt fine -- no dizziness or anything. They asked me some questions, and I don't think I knew the answers to any of them. I just remember going after the ball. I was down. Then, I was in the ambulance.

"I really feel like if I didn't have a headache, I think I'd be feeling OK. Obviously, where I got hit hurts. Outside of that, I'm all right."

Walker had a battery of blood tests, a CT scan and hourly wake-ups for blood pressure and concussion exams, so mostly he was exhausted. He was discharged from the hospital around 11 a.m..

"I think it could have been a lot worse, really," Walker said of the collision. "Fortunately, Church has soft knees ... There's nothing really that could have been done [to avoid it]. I didn't see him, I didn't hear him.

"As soon as I went for the ball, that's the last thing I remember. Then I blacked out. ... Fortunately it's not as bad as I guess it could be."

Bobby Crosby started for Walker at second base last night after six consecutive starts at shortstop, where Ronny Cedeno returned Saturday.

Russell said he has not thought beyond this road trip, but Aki Iwamura will not get recalled from Class AAA. Although, he added, Andy LaRoche might play second base in a few days.

"Getting close. Still need to continue to do some work," Russell said of LaRoche, who has been working at other infield positions since before Pedro Alvarez was recalled from the minors 12 days ago.

"But I don't think he's too far away. The good thing that's going to help Andy is, he'll have a stretch at home where he can really work every day.

"Here [on the road] it's a little tougher to do it the way you want to. He's getting pretty close."

Russell noted that Justin Thomas' eighth-inning debut Friday, the inning after Walker's injury and a seven-run Oakland outburst in the seventh, was not a good barometer for the left-hander claimed off waivers from Seattle shortly before Halloween.

"Very tough [situation]," Russell said of an inning in which Thomas gave up two earned runs and finished with an 18.00 ERA.

"Got him up twice earlier [to warm up]."

But he was encouraged by Thomas' fastball and his attack against left-handed batters.

"I think that'll be a plus for us," he added of the reliever recalled this past week from Indianapolis, where Thomas had a 1.30 ERA and 34 strikeouts against three walks in 342/3 innings.

• Church, like Walker, felt fortunate -- for both Walker's health and his own. Had his right foot been planted at the time of collision and his spikes caught hold, the torque from their impact might have done serious damage to both his knee and Walker.

• The Pirates wore black-on-black, 1970s-style uniforms with gold stirrups and gold ballcaps with circular, black stripes in a throwback night on which the A's honored their champions from that decade, including Vida Blue, Bert Campaneris, Ray Fosse and more. Said Ryan Doumit of the duds: "Black pants? I haven't seen that since Little Leagues."

• The first pitch in this throwback night came from Mrs. Fields, the former Debbi Sivyer, who was a ball girl for the A's back in the 1970s.

Colin Dunlap's blog on the Pirates is featured exclusively on PG+, a members-only web site from the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.