The former Tottenham boss took to social media after Dortmund's 5-1 aggregate win over the north London side.
Indeed, Ardiles couldn't help but praise Dortmund and made the confident claim that the Bundesliga outfit are the best to have graced White Hart Lane this season.
He also feels Tottenham now have the benefit of concentrating fully on the Premier League.
Dortmund were 3-0 first-leg winners and then won 2-1 on Thursday night in the capital.
Borussia D: By far, the best team to play at The Lane this season. Good luck to them. Us: Now concentrate fully in the PL. COYS— osvaldo ardiles (@osvaldooardiles) March 18, 2016
A follower, meanwhile, responded to Ardiles agreeing that Spurs' conquerors are 'absolutely world class.'
The Argentine agreed and hopes Borussia Dortmund go on to win the Europa League.
@osvaldooardiles Absolutely world class. Definitely belong in the CL. Hope they go on to win it.— Jas Dhoofer (@JasDhoofer) March 18, 2016
Tottenham host Bournemouth in the Premier League next up on Sunday afternoon, having beaten the Cherries 5-1 in the reverse fixture earlier this season.
Eddie Howe's men are in much better shape now, of course, so the north London side need to avoid complacency in their hunt to close the five-point gap on Leicester.