Mensah ends his four-year stay as he amicably terminated his contract that was supposed to end June 2013.
The Ghana captain moved to the Stade de Gerland in 2008 but has become a peripheral figure at the club which helped them to reach the decision.
Injury problems have seen the 29-year-old defender's performance level drop in recent times and he is now on the look-out for a new club after the club agreed to terminate his five-year contract a year before its conclusion.
"I will be leaving Lyon this summer, but for now I can't disclose where I will be going," Mensah said last month.
"My agent is working on my move so I will leave everything to him."
Recruited for 8.4 million Euros in July 2007, the Ghanaian international defender played 13 league matches for Lyon.
He spent time on loan at Sunderland in the 2009-2010 season and during the following campaign as well.