Leinster lock Toner has undergone ankle surgery for the issue suffered in Ireland’s 32-20 loss to England last weekend and will be sidelined for two months.
The dependable second-row has so far only missed six Test matches since Joe Schmidt took charge of Ireland in 2013, featuring more regularly than any other player under the Kiwi’s stewardship.
Ireland’s defence of their 2018 title took a hefty hit with that punishing loss to England in Dublin, and hooker Best has admitted Toner’s extended absence is another dent.
“Look it’s massive, he’s been a big part of what we’ve created here over the last while,” said Best.
“He’s a great player, and over the last 18 months, two years, he’s probably played some of the best rugby of his career.
“So to lose a player like that, and the intellectual property he brings around the lineout.
“You all know him, the calmness he has is a great thing to have around the team environment. So he’ll be a loss, as any great player is.”
Toner is Ireland’s third frontline lock injury in this tournament, with British and Irish Lion Iain Henderson missing with a finger complaint and Munster powerhouse Tadhg Beirne out with knee trouble.
Connacht’s Roux will share the burden of calling Ireland’s lineouts at Murrayfield, while provincial team-mate Ultan Dillane can offer pace and power on the ball from the bench.
“When these things happen it gives an opportunity to somebody else,” said Best.
“I thought Quinn Roux was great when he came on against England, he showed a lot of physicality, he’s been playing very well for Connacht.
“This is a massive opportunity for him, and also a big opportunity for James Ryan to step up, and also lead in that second-row.”
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When asked if Ireland’s second-row strength turning to an injury glut is rotten luck, Best continued: “I suppose it’s better happening now, and we’ll see just how much depth we have.
“We saw at the last World Cup what a couple of injuries can do. You need to make sure of the layer below that.
“And even when you look at Ultan Dillane on the bench, when called upon he’s been fantastic for Ireland.
“And it’s great to see him back involved. It’s unfortunate for the three boys, and to lose three world-class players in one position is difficult.
“But what an opportunity for the two boys to come in and show what they’re about, and to say ‘yes we’ve lost three world-class players, but we’ve actually opened our eyes to two that were right there as well’.
“And hopefully what depth we’ll have then – we’ll not just have four, we’ll have six.”
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