The 25-year-old went under the knife in a bid to remedy a troublesome hip injury last October, but is still only able to train individually.
'No fixed date when I'll be back'
"Obviously it's frustrating for me that the injury has not got better as quickly as I'd hoped," Johannsson told the club's official website. "It's not easy, but I'm giving it everything and am positive about the future. There's no fixed date when I'll be back in the team. We're taking it day by day, week by week and weigh up the pros and cons every day to decide which programme is best for me."
Johannsson made a bright start to his Werder career following his summer 2015 move from Dutch outfit AZ Alkmaar. He scored two goals in his first six Bundesliga appearances, but has not played since 22 September after a diagnosis of nerve irritation in his hip prompted surgery.
Bremen are currently 14th in the Bundesliga, a point above the relegation zone, with seven rounds of matches of the 2015/16 campaign left to play.