	At Doncaster in September, Cossack ran in the St Leger. He started favourite at odds of 4/5 despite doubts about his stamina and the fact that Pedley "declared to win" with his other runner, Foreclosure. Templeman attempted to repeat his Epsom tactics and sent Cossack into the lead from the start. By the straight most of his rivals were struggling but Van Tromp, ridden by Job Marson made steady progress and moved alongside the favourite a furlong and a half from the finish. Marson sent his colt past the leader and Templeman, realising he was beaten, eased Cossack down in the closing stages to finish second, two lengths behind the winner but well clear of the rest. On 12 October, Cossack appeared at Newmarket for the two and a quarter mile Cesarewitch Handicap for which he was set a weight of 118 pounds, including a six-pound weight penalty for finishing second in the St Leger. He finished fourth, behind the four-year-old Cawroush, who was carrying 98 pounds. His performance was creditable and reportedly led to speculation that he could have won the St Leger, had he not been ridden so aggressively.