The Nigeria international has not been offered a new deal following the expiry of his contract with the Smoggies.
Mikel Obi
Championship side Middlesbrough have confirmed the departure of John Obi Mikel from the Riverside Stadium.
The Super Eagles captain signed a short-term deal with the Smoggies in January after leaving Chinese Super League side Tianjin Teda.
The 32-year-old impressed during his short stay with the side and made 18 appearances, helping Boro to keep seven clean sheets, and scoring once.
Despite the effort of the former Chelsea player, the Smoggies missed out on a place in the play-off by a point after finishing seventh on the table.
Mikel has not been offered a new deal following the expiry of his contract along with three other players.
“Stewart Downing, Dimi Konstantopoulos, Andy Lonergan and John Obi Mikel are set to become free agents this summer," read a statement from the club website.
“The quartet are all out of contract and have not been offered new deals to stay on.
“Mikel and Lonergan joined on short-term deals last season, but Downing and Konstantopoulos are both long-serving players.”
Mikel has been included in Gernot Rohr’s 25-man provisional squad to the 2019 Africa Cup of Nations in Egypt, which kicks off on June 21.
Three-time African champions, Nigeria have been drawn in Group B along with Burundi, Guinea and Madagascar.