Methods are provided for collecting platelet-rich plasma. A disposable flow circuit is mounted to a fluid processing device having a fluid separation chamber and an injection device. A fluid containing plasma and platelets is continuously conveyed from a fluid source into the fluid separation chamber and processed to produce platelet-rich plasma. At least a portion of the platelet-rich plasma is automatically conveyed from the fluid separation chamber into the injection device, which is directly connected to a pump device such that at least a portion of the platelet-rich plasma from the fluid separation chamber is automatically conveyed into the pump device prior to being conveyed into the injection device. The injection device with the platelet-rich plasma is then detached from the disposable flow circuit.