Argentina only have two more chances to gain ranking points before May's pool draw.
Semi-finalists at last year's World Cup in England, the Pumas dropped from sixth to eighth in the world rankings after their 24-20 defeat by Wales in Cardiff last weekend.
They need to retain a top-eight position to avoid the prospect of being drawn to face two nations from the upper two tiers in the pool stages of the 2019 World Cup in Japan.
Argentina only have two more chances to gain ranking points before May's pool draw -- against Scotland in Edinburgh on Saturday and in next week's clash with England at Twickenham.
They will be overtaken by Scotland, currently ninth in the standings, if they fail to win at Murrayfield.
"It's an important match for us in every respect," said Ortega Desio. "We are under the pressure of having to win. It is our responsibility to improve on what we did against Wales."
The Pumas took a long time to get into their attacking stride against Wales, struggling in the scrums and conceding 11 first-half penalties.
Jet-lag, however, could have played a part in their downfall given Argentina travelled from Buenos Aires to play in Tokyo the previous Saturday for their 54-20 thrashing of Japan.
Scotland suffered their own disappointment last Saturday but played an impressive brand of open rugby before conceding a late converted try in a 23-22 loss to Australia
"Scotland were close to beating Australia and they are a team who have improved a lot in recent years," said Ortega Desio.
"They are orderly in defence and they always cause us problems.
"We cannot underestimate them. It would be a serious mistake."
Argentina have not beaten Scotland since a 13-12 World Cup pool win in Wellington in September 2011.
Pumas coach Daniel Hourcade has named an unchanged starting XV for only the second time in his three-year tenure, with former Toulon outside-half Nicolas Sanchez collecting his 50th cap.
Scotland coach Vern Cotter will want to guide his squad into the top eight before making way for Glasgow's Gregor Townsend in June and leaving for Montpellier.
Cotter boasts a 2-0 record against the Pumas, courtesy of a 21-19 win in Cordoba in June 2014 and a 41-31 victory in his first Murrayfield match as Scotland boss in November of the same year.
The New Zealander has made four changes, with Edinburgh blindside flanker Magnus Bradbury poised for a Test debut.
Grant Gilchrist has replaced injured lock Richie Gray, Fraser Brown has come in for hooker Ross Ford and Tommy Seymour has taken over from left wing Tim Visser.
Scotland captain Greig Laidlaw acknowledged the significance of Saturday's match by saying: "It's clearly very important.
"We know about the ranking points, but they will be in the back of our minds."
The scrum-half added: "If we concentrate on ourselves and play for the full game then we have a better chance of winning, and the ranking points will take care of themselves."