Manager Don Wakamatsu acknowledged before Sunday's series finale against the Blue Jays that he probably has written Branyan's name on a lineup card for the last time this season.
"It doesn't look real promising that he will finish out the year," he said. "We were hoping that after working out [in Toronto] for four days, he would feel remarkably better and we don't see that."
Branyan took pregame batting practice with the team and swung the bat well. But he was too sore on Friday to take grounders at first base, and he has yet to run full-speed.
"Looking at the big picture, maybe it would be best to go into the offseason and focus on getting stronger and not worry about what's going to happen when I swing a bat," he said.
For the first half of the season especially, opposing pitchers were the ones worried about what happened when the 33-year-old swung the bat.
He established career highs in home runs (31) and RBIs (76).
Most of his production came during a healthy first half of the season. He had 22 homers and 49 RBIs at the All-Star break.
"He had as good of a first half as anyone in baseball and merited consideration for the All-Star team," Wakamatsu said. "I think [he has] proven to the fans and to himself that he has a lot of potential. He had a tremendous year."
The scouting report on Branyan prior to this season was that he could not hit left-handers. But the Mariners gambled $1.4 million that he could -- and he did when healthy.
"I said it and people laughed at me, but his home run numbers per at-bat against left-handers were still pretty good, I thought," Wakamatsu said. "Sure, the strikeouts were there and the batting average wasn't that good, but the number of home runs he hit off lefties was a number that indicated to me that if he had consistent playing time, maybe it wouldn't affect him as much."
Branyan, who is eligible for free agency when the World Series ends, says he would like to return to the Mariners next season. But his first priority is to regain his health.
"I don't think this will be a problem," he said of his back. "I've been told that if I rest it properly and have proper maintenance, it could go away and I would never see it again."