Steven Gerrard says Rangers' opening five minutes in their 1-1 draw with Hearts "was the worst I've seen us" since he took over last summer.
The manager also warned if they repeat that against Porto in the Europa League on Thursday, "we could be in trouble".
Ryotaro Meshino put Hearts ahead after six minutes at Tynecastle, with Alfredo Morelos equalising before the break.
"We started really badly - wrong mentality, wrong attitude," Gerrard told Rangers TV.
"I said when you come to a place like Tynecastle, it's so important you compete and you earn the right and we didn't do that. If we had done that in the opening 20 minutes, we win this game 1-0."
A win would have returned Rangers to the top of the Scottish Premiership, but the draw means they end the weekend behind Celtic on goals scored after their city rivals' 6-0 thumping of Ross County.
"I thought we reacted well to going a goal down, but I'm really disappointed and frustrated at how we started the game," Gerrard said.
"We got a warning when they hit the crossbar and could have been a couple down in the opening 10 minutes."
James Tavernier's poor back header led to Hearts' goal, but although his manager acknowledged it was "an individual error", he suggested "that comes from how we started collectively".
Gerrard thought Hearts manager Craig Levein would be "really proud" of his side as "they maxed out" with the team they were able to field despite recent injury problems.
Winger Ryan Kent appeared for 30 minutes as a substitute after a month on the sidelines through injury, but the manager was underwhelmed by his side's threat in the final third.
"As an attacking force, we weren't at the races," Gerrard said. "Our creative players haven't come to the party, we haven't tested the goalkeeper enough and again Alfredo's bailed us out."
Gerrard will demand an improvement when Rangers visit Porto in their third game in Europa League Group G.
"To get a result there, we're certainly going to have to compete and do a lot of dirty work and fight and work so hard for each other and be in the right frame of mind," he added.