The 27-year-old Argentine made a sparking start to his Premier League career, scoring three times in his first five league matches.
But his form has come under heavy scrutiny in recent weeks following a string of poor performances and no goals since January.
Di Maria has also struggled with off-the-field issues after his £4million house was attacked by burglars in January who used scaffolding poles to try to smash in doors while he and his young family were eating.
However assistant manager Giggs believes British football's most expensive player will improve and become a "match-winner" again for United.
"He's a quality player and we'll be looking for him to produce because it is big game after big game now," Giggs said.
"Players get used to different leagues, sometimes quickly and sometimes it takes a bit of time.
"He had a really good start to the season but with players who take risks and who can win games it's always difficult to be consistent because they will try things that other players won't do.
"They're capable of doing that and that's why they're match-winners and the best players."
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