There have been plenty of frustrating moments for Iain Henderson this season, but the Ulster captain isn't hoping to see the back of this campaign anytime soon.

The second row had to wait until the end of November to get back out onto the pitch after thumb surgery in the summer, his return coinciding with Ulster's mid-season dip in form.

But after getting steady game time under his belt during the winter, he has found himself back in the thick of a Six Nations campaign with Ireland, and looking to take another step towards what would be a fourth title success with Ireland.

"This is where we wanted to be, where we planned and how we wanted our championship to go, so this is the fourth step of our plan," the 31-year-old says ahead of this Sunday's meeting with Scotland at Murrayfield (live on RTÉ2 and RTÉ Player).

"That's how we're approaching this game. Obviously, with the way the table's standing, Scotland are a huge challenge for us and we have to be wary of that and have been wary of it in our analysis this week."

The last 18 months have been peppered with injury setbacks for Henderson, who missed out on the Test series win against New Zealand last summer due to a knee injury, and used that time on the sidelines to also get some running repairs to a long-running thumb issue.

Having initially hoped to be back by October, the two-time British and Irish Lion saw his return delayed, sitting out of the Autumn Nations Series wins against South Africa, Fiji and Australia in November, although he did train with Ireland's extended squad during that time.

And he says it was an anxious time waiting for the final clearance to play.

"The late start was probably more frustrating for me, as it was kind of enforced management rather than an injury itself. Prior to the Autumn series, and during it, I trained fully here.

"As players we have huge faith in the 'S and C' staff to look after us, and the medical staff and physios and sports scientists that analyse our data, what we need to get back to, to ensure we don't get injured again.

"For me it was frustrating in that sense, I felt I just wanted to play immediately, but I know that all those guys have the players' best interest at heart, and to take yourself out of it emotionally and realise they want the best for us. I've full faith in them, so I'm just enjoying being back playing and we can hopefully get another game or two under my belt."

Having come off the bench in Ireland's opening two Six Nations games against Wales and France, making a big impact against the French in particular, he earned his 71st Irish cap from the start against Italy in Rome, taking the second row spot left vacant by the injured Tadhg Beirne.

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Bernard Jackman and Rory Lawson look ahead to Scotland v Ireland

Henderson is likely to remain in the engine room with James Ryan when Andy Farrell names his team for Scotland tomorrow, and says he and others have to step up and take the opportunities that injuries present.

"Leading into those first two games, I can't complain if I'm sitting behind Cheese [James Ryan] and Tadhg [Beirne], two world-class players.

"For me the focus was to prepare them as best as possible, and unfortunately for Tadhg it was the end of his tournament against France. I was genuinely gutted for him, but there lies an opportunity for someone to step in, and not only for me, but for someone like Ryan Baird to come on against Italy and make the impact he did, it's good to see him progressing and him doing well.

"I'm looking forward to the other opportunities I get, be it starting or off the bench,. You've heard me talking before about this environment, it's a special place to be and enjoyable to be involved, and a group pf people who want the team on the pitch at any one time to do better."

Scotland will be forced into a change at second row this weekend, with Jonny Gray expected to join his brother Richie at lock after the suspension for Grant Gilchrist, who will miss the rest of the Six Nations following his red card against France in Round 3.

The Scottish backline have grabbed the headlines for Gregor Townsend so far in the championship, but their pack have been going about their business with real efficiency.

And while Henderson says Gilchrist (below) will be a loss for the Scots, he expects Jonny Gray to come back into the side with a point to prove.

"Grant Gilchrist looks like a big leader for them, he looks like someone who adds a lot of tempo to their pack but along with a bit of aggression as well. Definitely in terms of lineout analysis you can see the guys really looking to him, he drives that.

"Jonny Gray has been massive for them over the past number of years. He'll be itching to get an opportunity to show, 'Look, I should be back in here.’

"I think they've been trying to build something there and I've been in teams where you're trying to build something, and you can feel it internally but maybe you're not getting the full results and I felt that's been Scotland in the year before this.

"You could see them in the last Six Nations showing glimpses of big games and big performances, but over the last six months you've seen them really tie these things together, and that's probably why they're an enormous threat for us this weekend. They definitely have been playing a more attractive brand of rugby and putting teams under massive pressure."

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Watch live coverage of Scotland v Ireland (Sunday 3pm) on RTÉ2 and RTÉ Player, follow our live blog on RTÉ.ie/Sport and the RTÉ News app, or listen to live commentary on RTÉ Radio 1.