The Florida-based Scot finished The Barclays event on the PGA Tour in New York with a one-under-par 70, leaving him four over for the tournament.
That was only good enough for a tie for 60th, 13 shots behind winner Patrick Reed, leaving Knox 10th on the World Points list for Ryder Cup rankings.
Meanwhile back in Europe, fellow wildcard contender Thomas Pieters of Belgium, who narrowly missed out on automatic selection after finishing ninth on the European Points list and 11th on the World Points list, stated his case for a captain's pick by winning the Made in Denmark title.
That victory came two weeks after the 24-year-old finished fourth at the Rio Olympic Games, and a week after a runner-up finish at the Czech Masters.
It is now out of their hands, leaving Knox waiting for a phone call from Clarke before the Northern Irishman confirms his three captain's choices at 12:30 BST on Tuesday.
Frustratingly for the 31-year-old, he sits just outside the nine automatic qualifiers, knowing that had he been a European Tour member when he won the WGC-HSBC Champions event in Shanghai last November, he would already have had the points necessary to make his Ryder Cup debut.
Instead the Invernesian is vying with Ryder Cup veterans such as Lee Westwood, Martin Kaymer and Graeme McDowell for a place in Clarke's team for the biennial clash from 30 September-2 October at Hazeltine, Minnesota.
Like the in-form Pieters, Denmark's Soren Kjeldsen and Ireland's Shane Lowry, Knox would be a sixth rookie - with Clarke expected to favour experience in his wildcard picks.
While US captain Davis Love III has a couple more weeks to mull over his options, what Clarke says is the toughest part of his job is nearly over.
"There is a huge amount of interest in our three remaining wildcards and whoever they are, they will be three fantastic additions to the nine guys we already have," said the Northern Irishman.
Michael McEwan, of Scottish golf magazine Bunkered, told BBC Scotland that while he hopes Knox will feature, he fears the weekend's results may have swung things away from the Scot.
"The way the team is shaping up at the moment, it's very rookie heavy so I think he's going to want to add in some experience and on that basis I would suggest Lee Westwood and Martin Kaymer are probably two of his three picks.
"Thereafter it is between Thomas Pieters and Russell Knox I would imagine. Until yesterday Russell was looking most likely to get it, but Pieters winning as he did in Denmark, allied to being second the week before and a strong Olympic performance, I think unfortunately he's just got the nod on Russell.
"I'd be amazed if he got picked at this stage."
Given the lack of Ryder Cup experience in some of the candidates, the fact Knox is based in Florida and plays on the PGA Tour could be seen as beneficial, but McEwan believes form will the most important factor in Clarke's three wildcard picks.
"I'd love to think that Knox's experience of playing in the States in front of American crowds and against the best American players would stand in his favour," he added.
"But form is a very important thing, and Pieters is the in-form player."
The European team will be announced at 1230 BST on Tuesday, 30 August.
It was a final chance to catch the eye of European Ryder Cup captain Darren Clarke before he confirms his three wildcard picks on Tuesday, but things did not quite go as planned for Russell Knox.