Streiff, claiming to be a 'family friend', said Schumacher, had 'very limited' movement but was working on sitting upright, and that 'long term... he could hope one day to walk with crutches.'
However, Schumacher's manager has disputed the comments, saying Schumacher faces a 'long fight' for recovery, and that Streiff is not a family friend.
'We need a long time. It's going to be a long time and a hard fight,' Sabine Kehm said.
'He is making progress appropriate to the severity of the situation,' she added, reiterating a statement she made a month ago.
Ms Kehm said Streiff was not a close friend of Schumacher and that his claims to have had contact with the two people named were 'factually wrong'.
'I cannot confirm that (report),' she said. 'I can only confirm that I do not know where Mr Streiff has his information from because he has no contact with us and he never has.'
Kehm was forced to make similar denials last month, when Streiff, who is himself wheelchair-bound since following a crash in 1989, commented on Schumacher's health.
Speaking on French Radio, Streiff said: 'It's very difficult. He can't speak. Like me, he is in a wheelchair paralysed. He has memory problems and speech problems.'
Streiff, 59, was seen visiting Schumacher when the German was in intensive care in Grenoble Hospital, France.
Schumacher, a very competent skier, was holidaying with family and friends in Meribel, where he owns a chalet, on December 29, 2013.
He was skiing with his 14-year-old son on a red piste, which is classed for intermediate skiers.
But shortly after 11am he left the piste and skied on to an off-piste area located in between the red run and a blue run, for beginners to intermediates.
It was here that he struck a partially-covered rock. He was not skiing fast but he lost control and catapulted 34 feet on to another rock, severely injuring his head.
After spending several months in a medically induced coma, Schumacher was transferred to Lausanne Hospital, Switzerland, in June and he is now being cared for at his home on the shores of Lake Geneva.