It's been 12 days since Jaso was placed on the seven-day concussion disabled list, which likely means he'll be transferred to the 15-day DL this week.
This is the third concussion of Jaso's career, though the backstop has said many times that he never before experienced such lasting symptoms until now, which includes buzzing in his ear each time he wakes.
"He continues to improve as far as how he feels after riding the bike and all," Melvin said, "but still until we actually get him into baseball activities, there's really no way of knowing how to forecast his schedule."
Jaso had a .415 on-base percentage in the 16 games before he was sidelined, production that has since been missing at catcher, where replacement Stephen Vogt has hit .188 with a .229 on-base percentage in 11 games spanning two stints with the A's this year.
Jane Lee is a reporter for MLB.com. Read her blog, Major Lee-ague, and follow her on Twitter @JaneMLB. This story was not subject to the approval of Major League Baseball or its clubs.