"I think range of motion indicated how he felt," Riggleman said. "Pitchers know their bodies, and when they wake up in the morning and move their arm around, they have a pretty good idea what they can do and what they can't do.
"I think he just feels he is not ready to throw."
Bedard, who last pitched on July 4 against the Tigers at Safeco Field, currently is on the 15-day disabled list with a "tight left shoulder." It is his second DL stint of the season, having been shut down from April 9-24 with inflammation in his left hip.
The 29-year-old lefty started his first season with the Mariners as the Opening Day starter and has compiled a 6-4 record and 3.67 ERA. But aches, pains and pitch-count limitations have resulted in him pitching just 81 innings.
Exactly when he returns is anyone's guess, but there's a good chance it won't happen before the non-waiver trading deadline. The Mariners are believed to be willing to trade Bedard, but it would be highly unlikely another organization would acquire him without a clean bill of heath.
"We don't have a specific timetable," Riggleman said. "We're not looking at trying to pitch him on the 31st. It will be based on how he feels. The 31st is kind of irrelevant when a guy has a tender arm."
The game plan going forward is to have Bedard play catch Monday, and if that goes well, he would play catch again Tuesday and possibly throw a bullpen session Wednesday or Thursday. Assuming there are no setbacks, he could then be slotted back into the starting rotation the final few days of the month.
"We're not going to test it out throwing until Monday, and hopefully, he will be ready to throw some firm catch. If not, we'll go from there," Riggleman said.
The Mariners acquired Bedard from the Orioles last February for five players, including All-Star reliever George Sherrill and outfielder Adam Jones.
Prior to this season, Bedard had been on the disabled list three times in his career -- the entire 2003 season following elbow surgery; May 22-July 18, 2005, with a strained MCL in his left knee; and last Sept. 9 through the end of the season with a strained right oblique.