The Welsh are in buoyant mood following their 28-25 win over England but know their depleted and battered team must front up again in Cardiff on Thursday against a Fiji side with nothing to lose.
"They are a very physical team," McBryde told a news conference. "They have big runners with gas and physicality.
"We know it's going to be a very physical battle and they won't hold anything back against us. It's their last chance of getting a big scalp."
Wales fought back to beat England by playing smart rugby in the closing stages of the match.
"The most positive thing for me as a coach was our problem-solving on the pitch," McBryde said.
"The replacements really did their job, brought a lot of accuracy. We finished strongly and turned things round in the scrum."
Preparations have been limited due to the turnaround and Wales coach Warren Gatland hinted that players who did not show enough intensity would be dropped for a game in which victory would put them within touching distance of the last eight.
"There's a bit of a balance with regards to how much work we can do between the games," McBryde said.
"But the intensity in training was there yesterday. Warren's words gave the players all the motivation they needed and we have the right mind-set."
The Welsh squad received a visit from former world boxing champion Joe Calzaghe at their training base on Tuesday evening.
"It was good for the boys to talk to Joe," McBryde said.
"He has stayed loyal to his roots. He thrived on being the underdog. It was great to have a bit of respite from rugby and talk to one of the greatest boxers in the world."
Fiji beat Wales at the 2007 World Cup, their only win over the Welsh in 10 meetings, but McBryde said the mentality in the side now was completely different.
"It is the resolve we have, the consistency in the squad and the resilience that is in the team," he said.
"The players have been there before."
The diminutive Matthew Morgan will start at fullback against Fiji following injuries to Leigh Halfpenny and Liam Williams and McBryde expects him to excite the home fans.
"Matthew's strengths are evident for all to see," he said.
"He's like a Welsh player of old, swinging the hips and producing that little bit of magic. I think the crowd will enjoy seeing that."
(Editing by Sudipto Ganguly)
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