A 2-0 defeat to Atletico Madrid over the weekend saw Ronald Koeman’s men drop to ninth on the La Liga table.
Barcelona have also lost their opening two games in the UEFA Champions League and are still reeling from the financial troubles that caused Lionel Messi’s exit to Paris Saint Germain in the summer.
Toure, who is currently an assistant manager at Russian Premier League side Akhmat Grozny, played for three seasons at the Camp Nou, winning two La Liga titles and the Champions League.
"It may be a difficult time for the club but my belief for Barcelona is strong," the 38-year-old posted on his official social media account.
"I will always be available for the club should they need me anytime as my heart is forever with the club, the people, and the fans.
"My time at Barcelona was one of the best memories of my playing career. The club decided to trust me when I was still a young player, yet to establish myself in the top leagues. I will forever be grateful to the club for what they have done for me."
Toure, who is a four-time African footballer of the year, also spent eight seasons with Manchester City where he won three Premier League titles, one FA Cup and two League Cups.
He was a member of the Ivory Coast national team that beat Ghana on penalties to win the 2015 African Cup of Nations.
