Wiese led JG 77 in the opening phase of the offensive until 25 December 1944, when he was severely injured in a training exercise. Wiese and his wingman, "Feldwebel" (Sergeant) Hansch, took off at 11:20 a.m. on a training flight over German held territory. The plan was to meet up with I. "Gruppe" but the two failed to establish contact. Instead, flying at an altitude of , they encountered a flight of Supermarine Spitfires in the vicinity of Bottrop and Essen. In the resulting aerial combat, both Bf 109 G-14s were shot down, Hansch was killed in action while Wiese bailed out. He came down near Essen-Dellwig. His parachute only opened partially, resulting in a harsh landing, and loss of consciousness. Wiese was taken to a field hospital at Bottrop where he was diagnosed with a concussion and minor skull fracture. He spent the rest of the winter in hospital, and was replaced as commander by "Major" Siegfried Freytag. Their victors may have been Spitfires from the Royal Canadian Air Force (RCAF) No. 401 Squadron which claimed two Bf 109s from the "Stab" of JG 77 shot down over Duisburg that day. One of these victories was credited to Flying Officer John MacKay.