Brendan Rodgers has told Simon Mignolet he wants an immediate response to the goalkeeper’s glaring error against Ludogorets, with the Belgium international’s position as first choice coming under increased scrutiny.

The Liverpool manager had instructed his team to make a solid start to the Champions League tie against the Bulgarian champions on Wednesday only for Mignolet to present Dani Abalo with a third-minute opener when he fumbled a long-range shot from Marcelinho. Despite conceding that a bobbly pitch had made matters difficult for outfield players and goalkeepers during the 2-2 draw in Sofia, Rodgers did not excuse Mignolet for the mistake entirely and admitted the 26-year-old’s confidence had to be addressed.

He has demanded a reaction from the goalkeeper when Stoke City arrive at Anfield on Saturday with Liverpool still seeking their first win of November. “As a goalkeeper you have to be able to let these things go,” said Rodgers of the fumble. “The goal was a massive setback for the team but we need to keep his confidence as high as we can. We have to look to the weekend and keep a clean sheet.”

Liverpool have kept only two clean sheets in 19 games this season, the last coming against Hull City on 25 October, with Mignolet’s form contributing to the defensive vulnerability. His error against Ludogorets may have been the most conspicuous of the campaign and has increased pressure on a goalkeeper whose inability to command his penalty area has caused obvious tension with Liverpool’s defenders. The club’s former goalkeeper Bruce Grobbelaar added his voice to criticism of the £9m signing from Sunderland before the Champions League tie in Bulgaria.

Mignolet’s distribution also alarmed against Ludogorets and has been a recurring fault this season. Crystal Palace scored after the goalkeeper sent a routine free-kick out of play at Selhurst Park on Sunday.

Liverpool’s home defeat by Chelsea concluded with Mignolet slicing a pass intended for Martin Skrtel out for what would have been a corner but for the referee blowing for full-time.

Given Rodgers placed great store on José Reina’s passing ability when he first arrived at Liverpool as manager, before replacing the Spaniard in 2013 with Mignolet, who initially impressed during the team’s challenge for the title, the Belgian’s form represents a serious concern to the Liverpool manager. So, too, the lack of serious competition offered by Brad Jones, who has made only 23 appearances for the club since signing in August 2010.

Jones’ prospects are improving amid Mignolet’s troubles but, with interest in the former Barcelona keeper Víctor Valdés not developing into a transfer, Liverpool may have to pursue an established goalkeeper when the window reopens. January is a notoriously difficult transfer market, although Petr Cech’s future at Chelsea is in doubt after he lost his place to Thibaut Courtois and Marc-André ter Stegen, who was linked with Liverpool before joining Barcelona, has yet to secure a regular role for Luis Enrique’s team.

One player who did enhance his first-team prospects in Sofia was Rickie Lambert, who scored for the second game in succession with Mario Balotelli sidelined with a groin problem. Rodgers admits the England international’s work-rate is exactly what Liverpool require as they seek to drag themselves back into form.

The Liverpool manager said: “I am so pleased for Rickie because he has had to be patient and bide his time. He ran himself into the ground against Ludogorets. That is what I am looking for now; I am looking for footballers who have the mentality to work their socks off. It is about the moment we are in.

“There are times when you are doing well and can put all of your technical players in the team but when the confidence is low it is important that your team is made up of those guys who are going to work and press. The two full-backs [Javier Manquillo and Glen Johnson] were strong, I thought Lucas and Joe Allen were outstanding in central midfield, they showed good composure and nicked the ball when it mattered, and Steven Gerrard at No10 gave great support to Rickie.

“Rickie held the ball up well. As soon as Rickie got his first goal [against Palace on Sunday] he was a different person. You could see him at the training ground with a spring in his step, shoulders high, chest out. Ludogorets was a good result for us but only a small step in terms of where we need to go.”