He was on first base via a single in the fifth inning when he ran toward second base on a ball Jose Lopez hit to left field.
"I wasn't sure if the ball would be caught, so I stopped," Branyan said. "Somehow, I just tweaked it [his back]. I have a little history with the same thing, like once a year, you know. It normally happens early in the season and takes about four or five days to come back."
With Wednesday night being the fifth game he has missed, Branyan said there is a "good chance" he would return to the lineup for Thursday afternoon's series finale against the Rays.
"Russell is still a little stiff, but he's improving," manager Don Wakamatsu said. "He's going to take a couple of swings probably in the tunnel here [on Wednesday] and he'll come in early tomorrow for batting practice. Hopefully, it will be a dramatic improvement and he will be in the lineup. If not, we'll look at the Anaheim series for him."
The Mariners begin a two-city, six-game road trip on Friday night against the Angels in Anaheim.
Branyan, who has been given an opportunity to play virtually every day, is batting .273 with two home runs and three RBIs through his first 10 games.
"I wasn't doing my best," Branyan said, "but everyone is making adjustments. I wasn't swinging my best, but I am seeing the ball great. I thought I was starting to come around.
"It's up to me to go out there every day and put up numbers and play like I'm capable of playing. It is frustrating to have any type of hiccup, you know. I want to be out there every day. I want to be hitting every mistake, every strike into the gap. I feel like I'm capable of putting together a good, solid year."
Meanwhile, the Mariners medical staff is in the process of putting Branyan on a program that will improve his core strength and help prevent a recurrence of the lower-back problems.
In other medical news, left-handed starter Ryan Rowland-Smith, who missed his second straight start on Wednesday night, had an MRI on his left elbow.
"He has some fluid in the joint but no structural damage," Wakamatsu said. "That is good news, but probably means he needs a week or so more of rehab time. I don't know when he might start throwing again or if he will go on the road trip."
Regardless, Rowland-Smith won't be ready to come off the DL on Sunday, which is when he is eligible to be activated.