But the 23-year-old right-hander didn't have to go on the disabled list and says the brief rest seems to have helped,
"I threw everything and it felt good," Walker said after his bullpen session.
Manager Scott Servais is still awaiting final word from the trainers and pitching coach Mel Stottlemyre Jr., but remains confident that Walker will be ready to slip back in the rotation.
"He was the first one waiting for Mel to show up today, so he's anxious," Servais said. "I'm expecting everything to be a go."
Wade Miley also threw a bullpen on Sunday and remains on track to come off the 15-day DL to make Wednesday's start against the Pirates.
With LeBlanc throwing six scoreless innings in Friday's 4-3 win, Walker feeling better, Miley coming off the DL and Felix Hernandez starting to gear up his throwing and likely to rejoin the club in mid-July, the Mariners will soon have extra rotation options to supplement the healthy trio of Hisashi Iwakuma, James Paxton and Nathan Karns.
"It's good that we'll actually have to make some tougher decisions here," Servais said. "Obviously what Wade LeBlanc did the other day was a huge boost for us. He's certainly got great pitchabilty and we feel good about running him out there. We'll have some discussions with Jerry [Dipoto] and the coaching staff and we'll have a plan."
That plan won't likely include going with six starters at any point, however.
"We'll look at it and look at the schedule and when Felix is actually back in the picture," Servais said. "We'll see. My initial response is no. I'd like to get the real Taijuan back, have Paxton going, get Karns on track, Kuma is there, Felix is coming. Then you're kind of where we were early in the season."
• Catcher Jesus Sucre, who is on the 60-day disabled list after fracturing his right leg during winter ball in Venezuela, has begun a Minor League rehab assignment with the Mariners' Arizona Rookie League team. Sucre, who played 81 games for Seattle over the past three seasons, went 1-for-2 with an RBI in Saturday's 6-5 win for the AZL team and is 4-for-10 with three RBIs in four games since being activated on Monday.
• Former first-round Draft pick Danny Hultzen has also begun a rehab assignment with the Rookie League team in Peoria as he works back from shoulder issues that have wiped out most of his last three seasons. Hultzen appeared in two games in relief this week, allowing three hits and one run in two innings.
• Center fielder Kyle Lewis, this year's first-round pick, has hit .200 (7-for-35) with three doubles, five walks and one stolen base in his first nine games for Short-A Everett going into Sunday's action.