Gareth Southgate pledged to stick to his principles after Spain delivered an uncomfortable reality check at Wembley but admitted he was unsure whether England had time to become genuine Euro 2020 challengers.
England were surprise World Cup semi-finalists in July, riding a wave of euphoria back home, but their 2-1 Nations League defeat on Saturday was their third consecutive loss.
Even during their morale-boosting run in Russia, manager Southgate warned there was still work to do and the performance at Wembley underlined that message.
Marcus Rashford struck early for England but Saul Niguez levelled for Spain moments later and Rodrigo scored the winning goal later in the first half.
Substitute Danny Welbeck saw a stoppage-time leveller controversially ruled out, meaning England head into Tuesday's friendly against Switzerland reeling from three successive defeats in all competitions for the first time since 1988.
Spain, who bowed out in the World Cup last-16 after a torrid campaign, nevertheless showed the benefits of a long-established identity and a level of creativity sorely lacking in England's midfield.
Southgate said he was unsure whether his side could close the gap to the top teams before the next European Championship, in which the semi-finals and final will be played at Wembley.
"I think we've got some players who can and have shown tonight they can perform at that level, and there's some that are still a work in progress," he said.
"We have got 19 matches, it's not very long, but, in my opinion, we have got the best group of players in the country here.
"I think we have got to keep faith in the way we're trying to play, otherwise we go back to what we did historically and there's no way I believe we'll ever be a top team if we do that," Southgate added.
Southgate plans to rotate his side at the King Power Stadium in Leicester and intends to bring in reinforcements from the Under-21s squad.
Manchester United defender Luke Shaw left the field on a stretcher against Spain after a heavy fall but said he was "doing fine".
Tottenham full-back Kieran Trippier said there was no reason for alarm despite the defeat, which follows losses to Croatia in the last four in Russia and to Belgium in the third-place play-off.
"It is not a concern," he said. "We are building and that is all we can do, play against these teams. We want to test ourselves against the best and certainly tonight we put up a fight.
"We knew it was going to be a difficult game. These are the teams we want to play against."