Manchester United have accepted they need another front player to help solve the scoring problems that have contributed to Louis van Gaal’s job being under intense scrutiny and led to an admission from Wayne Rooney that he is not playing well.

Van Gaal admitted after last week’s 2-1 home defeat to Norwich City that he was worried about his job security and one of the reasons for that has been the team’s lack of goals, scoring only four times in their past seven matches at Old Trafford.

United could not prise Sadio Mané away from Southampton in the last transfer window and are not optimistic about the chances of resurrecting that deal midway through the season. However, Mané remains a target for the end of the campaign.

Another player who has been discussed behind the scenes is Yoshinori Muto, a Japan international who turned down the offer of a five-year contract at Chelsea to sign for Mainz this year and has had a productive first season in the Bundesliga. Chelsea had offered to pay FC Tokyo around £3m but Muto, now 23, decided to move to Mainz because he felt there would be more first-team opportunities in Germany.

United are also in the market for another centre-half but, having seen the way Everton repelled Chelsea’s advances for John Stones, they are aware the Merseyside club do not want to let him go and that the Premier League’s new television package means clubs that once sold their better players are no longer under the same financial pressure.

Van Gaal’s team have the joint best defensive figures in the league as they head to Stoke City on the back of a run of three successive defeats that has increased the pressure on the manager. Less impressively, they have scored only 22 goals in their 17 games, fewer than Crystal Palace and the same number as Bournemouth.

The league leaders, Leicester City, have managed 15 more and Rooney, with only two, admitted he was off form. “I know that I have not been playing well and I’m working hard to try to improve and do my best for the team,” he said. “It’s not nice when you are getting criticised after every game.”