Nichols originally joined the show as new recruit Ashley Seaver following the departure of 'JJ' Jareau (A.J. Cook).
"I think it was unfortunate, because they look so much alike that people rejected Seaver because she seemed like she was a replacement for JJ," Messer told Entertainment Weekly. "As far as I'm concerned, she is a part of this team [and] I don't want her to just disappear."
The producer insisted that Nichols will not leave the CBS drama in the near future, despite A.J. Cook's return in the recent season finale.
"No, [A.J.'s return] doesn't necessarily mean [that Rachel is leaving]," she said. "Honestly, they're not the same character."
Rachel Nichols previously claimed that she understands fan criticism of her character Seaver.
"I get [why some fans] think she's useless or doesn't do anything," she admitted. "But you'll get to see more of Seaver... and you begin to understand that although she's new, there's a reason she deserves to be part of the team."
The seventh season of Criminal Minds will air on Wednesdays at 9/8c on CBS in the fall.