City enjoyed long periods of dominance but substitute Daniel Bogdanovic was allowed room chase down a long ball and fire past Shay Given with seven minutes remaining, before Martin Petrov grabbed an 88th minute equaliser.
Toure was withdrawn following a tangle defending a Barnsley corner, but didn't appear to be in great discomfort as he departed down the tunnel.
The visitors started brightly and Tykes full-back Bobby Hassell headed Emmanuel Adebayor's header off the line from Shaun Wright-Phillips' corner after 10 minutes.
In the 16th minute, Barnsley striker Jon Macken failed to punish his former club when he met Martin Devaney's cross, only to head over from six yards.
After 22 minutes Luke Steele completed a fantastic double save to keep the game level, first pawing away a Craig Bellamy effort from the left-hand side of the area, then responding to deny Adebayor's follow-up from close range.
City continued to enjoy the lion's share of possession but Barnsley midfielder Jacob Butterfield gave the visitors a couple of nervous moments before the break
The 19-year-old forced Given into save of the half after 39 minutes and rattled the Irishman's crossbar three minutes before the break. Jamal Campbell-Ryce was first to the loose ball and curled his shot narrowly wide.
A lively start to the second half saw Adebayor spur a golden opportunity, shooting tamely at Steele following a surging run from substitute Pablo Zabaleta.
Immediately Barnsley broke to the other end of the field and Macken failed to capitalise on an embarrassing slip from Toure.
After 52 minutes Robinho scooped immaculately over the Tykes back line and Adebayor lifted an effort onto Steele's crossbar, before somehow failing to convert the rebound with the goal at his mercy.
Two minutes later the home side's crossbar was again tested, this time by a rasping Robinho drive following Zabaleta's cut back.
In the 74th minute City broke from a Barnsley corner and Adebayor played Bellamy through on goal, only for his strike partner to waste a glorious chance and fire into the side netting.
Bellamy almost made amends three minutes later, arrowing a free-kick towards the top corner for Steele to scramble behind.
Zabaleta then crossed a cleverly worked short corner for Micah Richards to fire over.
Bogdanovic sent Oakwell into raptures shortly after, but Simon Davey's men could not hang on when Stephen Ireland engineered space in the penalty area, crossing for Petrov to finish from close range.