Bernard Jackman says there are still "big concerns" over aspects of Ireland's play after Sunday's victory over Scotland, a game they "had to win twice".
Ireland surrendered a commanding 14-point lead in the final quarter at Murrayfield, only to wrench back victory in the closing minutes, Ryan Baird and Iain Henderson combining to force a late penalty, which was slotted over from near the left touchline by Johnny Sexton.
The win pushes Ireland up to second in the table, albeit the current standings are somewhat distorted by the postponement of the France-Scotland game in Round 3.
"It was a game we had to win twice. Which is a little bit crazy," Jackman told Morning Ireland on RTÉ Radio 1.
"Luckily, we got away with it, thanks to Johnny's composure in nailing that kick in the final few minutes.
"There's still big concerns. Defensively, we missed double the amount of tackles that Scotland did. And this was a game where Johnny Sexton was 100%, Finn Russell didn't kick well, they ended up having to put Stuart Hogg into 10 and take over the kicking. Plus, they'd to put a number nine in at back-row, such were the injuries they had.
"And we had pretty much exclusive lineout ball from them. Their lineout completely malfunctioned and in fairness, Paul O'Connell's defensive lineout is top class.
"In the games we've played in the Six Nations, we've dominated possession yet we've had a really high level of missed tackles. It was good to hear Johnny talking about it because I've felt up until now they've been covering over it.
"It's a short turnaround so hopefully we can make improvements there because anyone who watched England-France on Saturday, it was a different level altogether."
Should Ireland conclude their 2021 campaign with a win over England next weekend, it will put a fine gloss on a tournament that had looked like a write-off early on, after two sickening losses against Wales and France.
Despite the glitches in performance thus far, Jackman feels Ireland are well capable of beating Eddie Jones' side, noting that several players are hitting the peak of their powers.
"No disrespect, the games we've won so far are like Aidan O'Brien winning in Dundalk. It's the Epsom Derby, it's Willie Mullins going to Cheltenham - that's what England is. It's a different level altogether, it's the marker we should be setting ourselves, England-France is where we should be competing. So, it's a huge game.
"That win will give self-belief. They got a little bit of belief from Italy but that's a better win in terms of the opposition.
"They're well capable of winning (against England). Some of the players are playing outstandingly well - Iain Henderson, Tadhg Beirne, Robbie Henshaw, Tadhg Furlong. We have lots of really good players.
"The reason pundits are getting frustrated is down to the content and cohesion of the team. England will be a really good test for us and hopefully we match up to it and overcome it."
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