Four of five tests showed on Monday that Minnesota Vikings' quarterback Tarvaris Jackson was recovering from the concussion that knocked him out of the game against San Diego, and he even showed a sense of humor when he arrived at team headquarters in the morning. "He said, 'Hi, I'm Donovan,' " coach Brad Childress said of his first conversation with Jackson the day after a scary injury. Jackson was just joking about thinking he was Donovan McNabb, of course, making light of a serious situation in the second quarter of the Vikings' 35-17 victory over the San Diego on Sunday. The second-year quarterback was injured after scrambling on a play and taking a hit to the head as he dived to the turf. Jackson said he was knocked unconscious, and he was frozen on the ground in a peculiar position, with his right arm sticking straight out.