Clement would probably be fit to start on Friday, but the Mariners are slated to face Baltimore left-hander Garrett Olson. If Clement appears in a game before Saturday, it will most likely be in a pinch-hitting role.
Kenji Johjima and Jamie Burke will continue to see time behind the plate in Clement's absence.
"I am going to play him against some left-handers, but based on talks with the trainers, we were going to give it to Friday, but we face a left-hander," Riggleman said. "I'm trying to give Johjima and Burke some playing time and if I don't do it against a left-hander, I don't know when I am going to do it, so he may not play [Friday]."
Clement's throwing session on Thursday came nine days after a foul popup partially tore off his right thumbnail and three days after he last tested the thumb in a game.
Clement was slotted as Seattle's designated hitter on Monday night against Texas, but went 0-for-4 with a strikeout, two groundouts and a flyout. Clement said that throwing originally caused him the most pain, but swinging eventually became equally painful.
"It makes more of a difference because it's my bottom hand and the top hand comes down when I swing, so I wasn't getting the extension that I wanted," Clement said.
But most of the pain that Clement felt when throwing and swinging has subsided. So, at the latest, Clement should be catching again on Saturday against the Orioles, who are scheduled to start right-hander Jeremy Guthrie.
Of course, catching is how Clement hurt his thumb in the first place and there are numerous factors besides foul popups that could aggravate it, but Riggleman isn't as concerned as he would be if it were Clement's left thumb.
"The potential [to suffer a thumb injury] is there so much of the time for those guys," Riggleman said. "I'd be more concerned if it was on his left hand, because he'd be taking a pounding, pitch after pitch. The only thing that might happen is a foul tip might catch it, but he should have his hand behind his back to protect from that happening."