Injuries have marred Schweinsteiger's time in England and he has missed United's last seven games in all competitions with a knee problem, but Van Gaal said a consistent run in the side would allow him to get back to his best.
"I had to convince the board to buy him, because he's a very good player and he always gives a team more balance," the manager told the club's website (www.manutd.com).
"Manchester United has bought him even though he is now 31.
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"Bastian has been unlucky because he picked up an injury at a time that he was playing very well -- he was improving.
"He played very well at Wolfsburg and then began to reach the level he showed at Munich -- I think he can (get back to that level)."
Fifth-placed United's 2-1 away defeat at relegation-threatened Sunderland in the Premier League on Saturday saw the gap widen to six points between United and fourth-placed Manchester City, currently in the last spot for Champions League qualification.
(Reporting by Simon Jennings in Bengaluru; editing by Katharine Houreld)
