Steven Gerrard says "individual basic errors of defending" - not tactics - were to blame for his side's 4-3 Europa League loss to Spartak Moscow.
Rangers were ahead three times before a defeat that drops them to third in Group G, with Spartak now second.
"We are bitterly disappointed with how we defended," manager Gerrard said.
"If the problem was tactically then I would have looked to change formation or personnel. The goals we conceded were nothing to do with tactics."
Rangers, whose 11-game unbeaten run in the competition came to an end, are a point below Villarreal, who drew 0-0 away to Rapid Vienna, with the Spanish side next visiting Ibrox.
"It is still wide-open and it will go to the wire, which is what we predicted at the beginning," Gerrard said. "Tonight's result makes the challenge a bit more difficult and Villarreal becomes even bigger now and more exciting."
A Roman Eremenko own goal gave Rangers a great start and they were 3-2 ahead at the break thanks to Daniel Candeias and Glenn Middleton.
But those were cancelled out by Lorenzo Melgarejo, a Connor Goldson own goal and Luis Adriano before a Sofiane Hanni strike deflected in off Goldson.
"I think we attacked very well and I thought we were very dangerous and countered very bravely and got our rewards for that to be in control of the game at half-time," Gerrard said.
"But, for me, football is about levels and, if you don't defend properly and you don't do the basics well enough, high-level players and high-level teams normally punish you and that was the case.
"We didn't do the basics well enough, or clear our lines at the right time. At times, we weren't in the right positions.
"People who have had a lot of praise and have done really, really well to get us to this stage just didn't do the basics well enough."
Alfredo Morelos thought he had given Rangers a 4-2 lead only to be denied by an offside flag that Gerrard thought was raised in error.
"Normally, coming away to a place like this to get three goals, you at least expect to get a result," the manager added. "We should have had four goals, but that is another story, but we are bitterly disappointed with how we defended tonight.
"We had a terrible five minutes just after the break and we were punished for it."
Riancho unsure of Spartak future
Spartak interim head coach Raul Riancho dedicated his side's victory over Rangers to "my father, who recently passed away" and praised his players for having the "character" to come back from behind three times.
"The main thing is that Spartak retain the chance of reaching the play-offs," he said.
Spartak's supporters were left unhappy with the sacking of Riancho's predecessor, but the coach praised the home support for helping his players "grow wings".
Riancho said that switching to a more attacking 4-3-3 formation had helped his side create chances - but also created problems in defence.
The Spaniard says he does not know how long he will be in charge but insists he would not be staying as assistant if he does not get the job permanently as he believes he has enough experience to be head coach.