According to A's manager Bob Geren, Harden threw 25 times before Thursday's game against the Mariners and reported no pain in his shoulder.
"He threw from about 80 feet and said he felt good, so that's good," Geren said. "I don't think there is an actual schedule for him right now. He's day-to-day, so we will see how he feels tomorrow."
Harden, who has been riddled with injuries over the last four seasons, has pitched in two games this season, posting a 1-0 record with 0.82 ERA.
Harden first experienced soreness while throwing a bullpen session upon his arrival in the United States following his team's 18-hour flight from Japan at the end of March. In his last outing against Boston on April 2, Harden was forced to leave after just five innings because of inconsistent velocity on his pitches stemming from the shoulder strain.
In other injury related news, Geren announced that starting pitcher Justin Duchscherer reported no pain a day after throwing a bullpen session. According to Geren, Duchscherer will throw another bullpen session either Friday or Saturday and is expected to make a start in Las Vegas on Monday.
Duchscherer, who suffered a strained right biceps muscle on April 5, said he felt real good during the bullpen session and experienced no pain.
With Harden and Duchscherer on the disabled list, the A's have turned to lefty Lenny DiNardo, who started on Thursday against the Mariners, and right-hander Chad Gaudin, who will make the start against the Royals on Friday.
Jayson Addcox is a contributor for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.