Network Event Timing

When exactly is OnPlayerDisconnected/etc called, in relation to other operations such as Update()? Is it effectively 'multithreaded' (runs immediately regardless of the current program state), or is it called before/after Update() (but never during)?

Case: OnPlayerDisconnected removes a disconnected player from an array of players[]. If the array happened to be in-use by other code (ex: changing values) or expected to not change (ex: anything after reading players.Length), it may break (either read/write to the wrong player or error/etc).