Mikel joined Chelsea in 2006, making over 350 appearances for the club, but he has not featured at all under new manager Antonio Conte this season.
The 29-year-old is now expected to be let go by the Premier League leaders and is seemingly on the verge of a move to France.
“I saw Obi Mikel in London,” Rohr told Europe 1. “He is in advanced discussions with Olympique Marseille.
“He will leave Chelsea for free. This is a serious option.”
Mikel’s contract at Stamford Bridge is set to expire at the end of the season.
The Nigerian, Chelsea’s second longest-serving player behind John Terry, is yet to play a single minute under Antonio Conte and has hinted at a falling out with the manager over his involvement at the Olympic Games.
