Japan striker Yoshinori Muto will not have surgery to repair a right-knee ligament but will be out indefinitely, a source at his club Mainz said Sunday.

In his first European season, Muto had made an immediate impact with Mainz, winning a place on the first team and netting seven goals in 20 games.

But the former FC Tokyo man injured the knee in February, and aggravated it upon his return late last month. Manager Martin Schmidt had already ruled Muto out for the remainder of the Bundesliga campaign, but it appears the 23-year-old will be sidelined for the foreseeable future.

"We've decided against surgery and opted for conservative therapy," the source said. "He will stay in Japan until he is back to 100 percent, receiving treatment and doing his rehab work.

"There's no timetable for a full recovery. We want him to take all the time he needs to get himself right."