Edinburgh - Scotland lock Jonny Gray believes his side will be going up against one of the best teams in the world when they face Argentina at Murrayfield on Saturday.
The Pumas have built on their traditional forward-based game since being admitted to the southern hemisphere Rugby Championship in 2014.
Argentina have defeated Australia and South Africa and pushed world champions New Zealand hard before losing in Hamilton this year.
Both teams in Edinburgh this weekend will be coming off the back of narrow losses, with Argentina having gone down 24-20 to Wales in Cardiff last weekend while Scotland suffered an even slimmer defeat after being edged out 23-22 by Australia at Murrayfield.
"Are they up there with the best sides in the world now? I'd say so," said Gray of the Pumas.
"Argentina are a great team. They can attack from anywhere. Look at the players they have got -- guys like Agustin Creevy, some of their backs and their huge wingers, so they have some dangerous strike runners.
"They are always keeping the ball alive so you can never switch off.
"When it comes to facing them up front, in the scrum and in the line-out it's going to be a huge challenge. Across the board we have to be switched on.
"You just have to look at some of their recent results in the Rugby Championship to realise they are a world-class side. They beat South Africa and then pushed New Zealand all the way.
"We have to be on it from minute one to the final whistle. We need to be clever, we can't be coughing up ball to them."
Gray himself has been tipped to be included in coach Warren Gatland's squad for the British and Irish Lions tour of New Zealand next year.
He completed all of his 24 tackles against Australia but Gray said: "I don't look at numbers. As a defence we all work for each other. Whoever is there makes the tackle and whoever misses the tackle is there to help clean up.
"We play for each other, we play with a lot of heart, so it's a team effort, always.
"I'm just lucky I've got the coaches at Glasgow and Scotland who will sit down with me and show me where I can improve my game.
"It's really special getting to play for your country and to come up against some of the best second-rows in the world like we did at the weekend against Australia.
"It's a great opportunity to test yourself against these guys. I think I've got a lot to improve on and a long way to go before I'm at that level."