The Red Devils were forced to make a late quick move in the January transfer window for the midfielder after Christian Eriksen was ruled out until late April with an ankle injury.
Sabitzer has made Old Trafford arrival on loan for the remainder of the campaign, with United having no purchase option as part of their deal with Bayern National Daily can reveal.
The 28-year-old Austria international had struggled for playing time at Bayern this season, starting just seven games in the Bundesliga, but Muller believes his teammate still has a future with the German club.
Muller expressed shock at Sabitzer’s move to Old Trafford
‘The team was surprised,’ Muller told Kicker about Sabitzer’s late move to United.
‘It happened very quickly. I’m happy for Sabi that he’s moving to Manchester United, getting the chance to play there. Manchester are a huge name.’
‘He’ll be back in the summer. The chapter isn’t over yet.’
Muller also added that Sabitzer is ‘a cool guy and a great player’.
Speaking about his move to United earlier this week, Sabitzer said: ‘Sometimes in life you have to make quick and important decisions
‘From the moment I heard about this opportunity I knew it was right for me. I am a competitive player; I want to win and help the club achieve its aims this season.
‘I feel that I am at my peak as a player, and that I can contribute a lot of experience and energy to the squad. I am excited to start with my new team-mates and manager and to show my qualities to Manchester United fans.’