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Austin, having scored for the Rs in a 4-2 friendly win at the Kiyan Prince Foundation Stadium on Saturday, went in on Wan-Bissaka during an appearance on talkSPORT.
"Although Manchester United have signed [Raphael] Varane, their biggest problem is they need a right-back," Austin said.
"Aaron Wan-Bissaka is not up to the [required] quality. We played them the other day, and I know it was only a pre-season, but they need to go all out for Kieran Trippier.
"That's who they're crying out for. Aaron Wan-Bissaka can't defend!
"And his final ball is not what a centre-forward wants, it's not what [Edinson] Cavani wants, it's not what [Marcus] Rashford wants. They need to sign Kieran Trippier."
Austin came up against Wan-Bissaka and United and his goal came from a cross the former Crystal Palace man failed to cut out down his side.
It may have been a little harsh to blame Wan-Bissaka for QPR's equaliser, but he didn't cover himself in glory for the second goal scored by the hosts.
Wan-Bissaka was caught ball watching when the ball came to the far post and his slow reaction time meant the cut-back came to Lyndon Dykes, who put the Championship side ahead.
The clips have been shared by a QPR fan account in response to United fans who were outraged by what Austin had to say this week.
Wan-Bissaka has demonstrated his qualities in 1v1 situations against some of the best wingers in the world, but it's the attacking element of his game that many have questioned.
But in Austin's view, he isn't at the required standard for a team who title aspirations.
He stated: "With all due respect, if Aaron Wan-Bissaka is your right-back, are Man United going to win Premier Leagues and silverware? I'm not too sure.
"They need to strengthen there, definitely."
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