His Dundee United side have to beat Aberdeen and Celtic in the next seven days and look for favours from Motherwell's opponents to qualify for Europe via the SPFL Premiership following this draw, meaning their William Hill Scottish Cup final against St Johnstone on May 17 now looks the likeliest route back to the continent.
After dominating the early part of the match, and going ahead through Ryan Christie's well-worked goal, it came down to a disputed Farid El Alagui's equaliser to eventually cancel out Inverness Caledonian Thistle's advantage.
"The first half was brutal and the second was not much better than all right," Rankin said. "Inverness took the game to us and got a good goal but it was poor from our point of view. We let them get a free cross into the box and a free header.
"The cup final couldn't be any more important than it already is, whether or not Europe was in the equation. There has always been a place in Europe on offer but we want to win a trophy first and foremost.
"That said, the players threw themselves into tackles and put their bodies on the line, which shows the cup final was not in our thoughts. If anyone gets injured now, so be it, but the cup final will have no bearing on what happens next week."
With manager Jackie McNamara denied a dug-out presence through suspension, assistant Simon Donnelly was left to scratch his head over a puzzlingly poor first half. The influential Stuart Armstrong, back in his native city, was absent through injury and Gary Mackay-Steven, it transpired, should not have started the match due to a chest infection.
And, in fairness, Inverness looked like a team with extra spring in their step - buzzing with intent and invention from early in the match.
This may have been a reaction to last weekend's six-goal defeat by Celtic, as the previous time Inverness had suffered similarly at the hands of the champions, Dundee United then rubbed salt in the wound with a five-goal victory in the Scottish Cup.
On top of that, manager John Hughes, it transpired, was without central defensive pillars Gary Warren and Josh Meekings, as well as the injured David Raven, Richie Foran and James Vincent.
"We were lucky to go in 1-0 down at half-time as we didn't get anywhere near the standard we are capable of," Rankin added. "It was only due to the fact we defended well that we were even still in the game. The second half was completely different as we showed a tempo and intensity in our game and got the ball forward much more quickly. We deservedly got the goal and created another three or four chances which we should have done better with."
With Inverness's Carl Tremarco shifted into the unfamiliar centre-half role and attack-minded Danny Williams deputising at left-back, it had looked ripe for United to make mischief. Instead, early United pressure quickly faded and Caledonian Thistle took the lead after seven minutes. The move was a delight, as Greg Tansey swept a pass across field to Marley Watkins, who controlled and whipped in a perfect cross and 19-year-old Christie ghosted in to angle a header past Radoslaw Cierzniak with calm poise.
Christie would soon be delighting with his skills and passing, while Inverness as a whole looked like a team much more at ease with Hughes' favoured style of play.
Billy McKay, however, hesitated too long after Christie's superb pass, allowing Gavin Gunning to make a saving tackle.
Dundee United did have a chance or two of their own - Ryan Dow was denied by the excellent Dean Brill - and Inverness's failure to capitalise on pressure and possession would come back to haunt the Highlanders after 71 minutes.
A reshuffled United looked much more threatening as the second half opened - with the added aerial threat of El Alagui and Brian Graham from the bench eventually telling.
With 19 minutes remaining, Paul Paton's free-kick caused trouble in a crowded home box and, after a spot of aerial pinball, El Alagui forced the ball past Brill, who claimed he had been impeded. In the end, a draw seemed fair, but did neither side's European hopes much good - Inverness's are killed completely and Dundee United's now all but dependent on the Scottish Cup final.
For Danny Williams, one of the stand-outs on the day, the disappointment is tempered by realism. "When you weigh it all up, it's been an unbelievable season and while you always want to play more, it has been great to be part of," he said. "When I came here I said I wanted to improve and I've been part of a team which has finished in the top six again and reached a cup final. I've got another two years here and I'm happy to play wherever the gaffer wants me to.
"I like the responsibility of defending and it does allow me to get on the ball more. I was an out-and-out winger and one of my old managers, Lee Ashcroft at Kendall Town, suggested I could have more influence in that position. I do enjoy it."