Johnny Sexton believes Ireland will have to clamp down on his opposite number Finn Russell in order to forge a path towards victory.

The Irish side resume their Six Nations campaign against the Scots on Sunday, with the aim of trying to make it a second win from four rounds of action and build on the victory against Italy.

Scotland opened their campaign with a victory over England, impressing Sexton in the process, before suffering a setback with a 14-man loss to Wales and the postponement of their fixture against France.

But it's the French-based Russell, who has Racing 92 on his CV in common with Sexton, who will be among the chief threats to Irish hopes, the Ireland captain acknowledged.

"He's obviously a big threat for us, knowing that he's got a full box of tricks that he likes to pull out," said Sexton.

"He's obviously a threat to the line, he's got a good short kicking game and he can pull the strings if we let him and he's hurt us in the past.

"We haven't played against him in the last couple of times we've played Scotland, so again we've kind of had to go back and look at some old footage.

"But he's been in good form for his club and he's a massive threat like they have across their team, but him and (Stuart) Hogg are probably the standout guys. We have to be on our game to stop him."

Sexton is among a clutch of seasoned internationals to sign one-year contract extensions but while that span may appear brief, the 35-year-old accepts that longer-term deals are not an option at this stage of his career and added that he is "not motivated by contract" but rather by on-field success.

"It was agreed pretty quickly. I suppose when you get to the age I'm at, most guys in their mid-30s it's one year, see how you feel this time next year and see how you're performing, how the body's holding up and the mind's holding up and that's really it," he said.

"I always knew it was going to be a one-year-at-a-time job when I got to this stage. I'm delighted to continue the journey for another year and still very hungry to try and achieve success with Leinster and Ireland." 

While provincial and international matters are at the forefront, Sexton admitted that another motivator for the squad is trying to get as many Irish players in contention for a place on the Lions tour, should one go ahead.

"The next two (games) are pretty important when it comes to Lions selections. It'll help the Irish cause if we can pick up a couple of wins," he said.

"It'll help get more numbers on the plane and that's ultimately what we want. We want to get as many Irish people on that trip as possible, so it's definitely at the backs of our minds somewhere."

Follow Scotland v Ireland (kick-off 3pm, Sunday) via our live blog on RTE.ie and the RTÉ News app or listen live on RTÉ Radio 1's Sunday Sport. Highlights on Against the Head on RTÉ2 and RTÉ Player, 8pm Monday.