The 21-year-old winger, who only recently returned to action after recovering from a leg fracture suffered in August, has now sustained a hamstring injury.
The setback occurred shortly before City's win at Everton, and although the club remain hopeful he will feature again before the season ends, it marks another difficult chapter in what was expected to be a breakthrough year for the Norwegian international.
Bobb had already faced a lengthy absence earlier in the campaign, not only due to the initial leg fracture but also because of an ankle problem that delayed his comeback.
Initially tipped to take on a key role on the right side of the team's attacking trio, his progress has been halted time and again by unfortunate injuries. His latest issue now threatens to further limit his chances to make a lasting impact this term, though the club remain optimistic about his long-term potential.