Reid cut a frustrated figure under the tight tag of James Jordon, with the No.1 draft pick held to just 17 disposals and one clearance in the 24.19 (163) to 4.11 (35) loss.
It was in stark contrast to the opening three rounds, when Reid flourished with Elliot Yeo by his side as the Eagles opened the season with a 2-1 record.
With Yeo (groin) and Deven Robertson (suspended) absent against Sydney, Reid could only muster 10 disposals across the first three quarters before being moved to half-back.
Reid gave away a 50m penalty at one point when he didn't give the ball back to the right opponent, and he was left incensed late in the match when his teammate Reuben Ginbey copped a forearm to the head from Angus Sheldrick.
McQualter said it wasn't great Reid gave away a free kick, but he praised his young bull for the way he stood up for a mate.
"I've just been told that he (Ginbey) got hit in the head and Harley didn't appreciate that and stood up for him," McQualter said.
"I don't want Harley to give away free kicks, and we talk about that, but the fact he's trying to stand up for his teammates, it's a pretty good trait."
Reid's struggles with the tag were obvious, but he lacked support from his Eagles teammates.
"We didn't help Harley enough," McQualter conceded.
"We need Harley playing great footy for us ... so his teammates have got to help him do that.Â
"That's the first hard tag he's copped this year, so we'll have a look at it and we'll get to work on it. It wasn't quite the level he's been at the last few weeks, but that's what you get from a 20-year-old."
West Coast's comeback wins over North Melbourne and Port Adelaide had raised hopes that the club's darkest days were now behind it.
But with the triple-figure loss to Sydney representing West Coast's fifth-largest defeat in club history, the result is a major reality check for the rebuilding list.
McQualter conceded his team is not anywhere near the level of the AFL's best outfits, but he knocked back suggestions his players got ahead of themselves following their recent two-game winning streak.
Robertson will return for the Gather Round clash with Geelong at Norwood Oval, but Yeo will be touch-and-go.
Bailey Williams will be considered for the No.1 ruck role after Matt Flynn was completely outclassed against Swans big man Brodie Grundy (28 disposals, 33 hitouts, nine clearances, one goal).
