Emegha has just committed to joining Chelsea at the end of the season, which hasn't gone down well with Strasbourg fans.
The striker, 22, missed victory over Le Havre due to injury, but was booed by home fans when collecting a Player of the Month award. A banner was also unfurled in the stands reading: 'Emegha, pawn of BlueCo. After changing shirt, give back your captain's armband'.
Chelsea and Strasbourg are both owned by BlueCo, with many fans of the French club fed-up with the way they've been treated.
Meanwhile, Rosenior said after defeating Le Havre: "Emanuel Emegha was devastated, and I was too.
"I am very disappointed by what I saw, seeing a banner against one of last season's best players is unacceptable.
"My players deserve much better. They have an impeccable attitude and do not deserve this treatment. This is a pivotal season in which we will be playing in the European Cup, but it seems that a minority are unhappy with our performances.
"It won't change anything because I remain very proud of my players and Emanuel Emegha will remain captain as long as he is here. It must be emphasised that this does not concern everyone, but only a minority."