Oakland Athletics catcher John Jaso is likely to be sidelined another three to four weeks and perhaps for the remainder of the season as he recovers from a lingering concussion.Jaso flew to Pittsburgh on Monday to be examined by renowned concussion expert Dr. Micky Collins after the catcher experienced nausea, dizziness, headaches and vision problems when he tried to play catch last week."My brain is still injured, basically," Jaso said. "The good news is I'll be back 100 percent, and the question is when."He took a ball off his mask July 24 at Houston and complained of a headache. Initially, Jaso was placed on the seven-day concussion list the following day, then transferred to the 15-day disabled list on Aug. 8."You can't rush it. We won't rush it," manager Bob Melvin said. "That's a pretty dangerous situation when you're talking about somebody's vision and obviously a head injury. We'll take it pretty slow."The A's will give him as long as he needs to get right - even though they would love to have him for the pennant race as the club tries to defend its division title, and possible playoffs.Jaso is earning $1.8 million in his first season with the A's. He is batting .271 with three homers and 21 RBIs in 70 games. Jaso said Dr. Collins doesn't expect the concussion to end his career."First and foremost we're worried about him, and based on what Dr. Collins said he will recover fully, so that's the first thing that makes you feel better about it," Melvin said. "The timetable on this thing, we just don't know yet. We're certainly not going to do anything until he's able to do baseball activities, and that's when you get a better idea of when he can come back. And he's not there at this point. Whether or not he comes back this year, I'm not sure, we certainly hold out hope for that. But I don't think anybody can predict that."The A's thought Jaso was ready to push it last week. When it became clear he wasn't, the team sent him for further examination from Collins.Jaso stayed back from the team's recent road trip. While at the Oakland Coliseum to throw, Jaso became "woozy." He said he went up to the press box to watch the stadium crew change the configuration for the Raiders' NFL preseason game Friday when he lost his balance, and he has never had vertigo previously. His eyes are having a hard time focusing - and the tests from the University of Pittsburgh showed that."It would be unwise to go out and play," Jaso said. "When I make the wrong movement, it's not like I have another concussion but it re-aggravates the concussion that I have. ... It's tough. I really want to rush back."