Bollobás–Scott partition conjecture for Eulerian digraphs

Let $G$ be an Eulerian directed graph on $n$ vertices, meaning that its indegree equals its outdegree at every vertex. Bollobás–Scott partition conjecture. The edge set of $G$ can be partitioned into $O(n)$ directed cycles. The source presents this as a stronger version of the long-cycle conjecture; it states that the conjecture is open even for simple graphs.