Soto will essentially serve as a backup to Derek Norris, who will assume the majority of starts behind the plate. Stephen Vogt, still dealing with a bone bruise in his right foot, will only be used at catcher in an emergency situation.
The 31-year-old Soto has only appeared in 10 games this season because of multiple injuries, notably a torn meniscus in his right knee that required surgery. He's 9-for-38 with one home run in his limited time at the plate this season, and a .248 career hitter with 92 homers in 666 games with the Cubs and Rangers.
"He's a two-way guy, not one you would say is a defensive specialist or just an offensive guy," said manager Bob Melvin. "He's able to do both, and based on the last couple years, going from an everyday role to a non-everyday role, knows how to deal with that."
To clear a spot on the 40-man roster for Soto, the A's transferred first baseman Kyle Blanks to the 60-day disabled list.
Jaso, who missed the entirety of the second half of the 2013 season because of concussion symptoms, began experiencing them again -- including fuzziness, headaches and nausea -- two weeks ago when he took a hard foul ball to his face mask. The latter two have dissipated, but the fuzziness is very much still there.
"I've just kind of been muscling through the games and trying to power through, but the symptoms have kind of escalated these past few days, and it got to the point where it was a little iffy if I could keep going back there behind the plate and catch," said Jaso. "I think we're going to give it a little bit of time to calm down."
Jaso will keep in touch with concussion specialist Dr. Micky Collins, who treated him last year. But both are confident that the catcher's current symptoms are not nearly as bad as what he endured before.
"It was definitely worse last time," Jaso said. "We're more knowledgeable about it now, so we know when to let the symptoms calm down and go away, rather than going back there and wearing another one and then maybe being out the whole year. It's all about avoiding that."
"It's something that we have to be very careful of," said Melvin. "Now that he's actually come out and said that it's been an issue for him, we have to be proactive with that. It's not something we should mess around with, especially with his history."
In a separate deal, the A's also acquired Minor League catcher Bryan Anderson from the Cincinnati Reds for international money.
Anderson began the season at Double-A Pensacola, where he hit .343 with five home runs and 19 RBIs in 21 games. He was promoted to Triple-A Louisville on May 5 and hit .302 in 52 games with the Bats. The 27-year-old left-handed hitter was batting .315 with 10 home runs and 43 RBIs in 73 games overall. Anderson made his Major League debut with St. Louis in 2010 and also played with the Cardinals in 2012 and the White Sox in 2013. He is a .210 career hitter in 35 games in the Majors.