Manchester United interim boss Michael Carrick worryingly admitted that he has no timeline on the return of centre-back Matthijs de Ligt.A back injury – initially described as a minor issue by former United head coach Ruben Amorim – has left the Dutch defender sidelined since the start of December.Matthijs de Ligt was an ever present for Man United before suffering a back injury in early DecemberGettyAfter starting the Red Devils’ first 13 games of the season, De Ligt’s season came to a grinding halt ahead of the match against West Ham on December 4.The 26-year-old was expected to return for the clash with Wolves four days later however, four months on, the defender is yet to make his first-team comeback.Asked whether the former Juventus and Bayern Munich centre-back would return to action before the end of the season, Carrick admitted he had no idea of when De Ligt would be fit enough to resume playing.“It’s difficult to say, just because it’s taken that much time,” Carrick said.“With backs sometimes you think it’s all right and all of a sudden it’s not quite right.“We’re just being patient and working through it. We’ll give him time and try to get him back as quickly as we can, but it’s really difficult to say.”The news is also of concern to the Netherlands ahead of this summer’s World Cup.De Ligt was selected by national team boss Ronald Koeman for the internationals in September and November.But with the tournament a little under three months away and De Ligt missing out on the upcoming internationals, time is running out for him to prove his fitness.Carrick was further quizzed on whether De Ligt may need to undergo surgery in a bid to correct the issue.Michael Carrick says he has no idea when De Ligt will be ready to returnGettyDe Ligt has never featured in a league match under CarrickGetty“I don’t want to get into that at this stage,” he said.“We’ll try and do whatever we can to help and we’re working through that now.“I’m not trying to hide anything. He’s improving. It’s just not as quick as we all hope.”United are riding high after last weekend’s 3-1 win over Aston Villa which put them in the driving seat for Champions League qualification.And they could further strengthen their grip on the top three with a win at Bournemouth on Friday evening – live on talkSPORT.United hit three points above Aston Villa in the race for European qualification with Liverpool, Chelsea and Brentford also in the running.Michael Carrick has quickly turned around Man United’s fortunes with Champions League qualification looking likelyCarrick has eight games remaining to secure a top four finish and doing so would further enhance his chances of landing the head coach role on a permanent basis.The former United midfielder has lost just one of his nine matches in charge with his team picking up 22 points from 27 available.Whilst Carrick often displays a calm facade, he admitted he got angry with his players following the 2-1 defeat at Newcastle earlier this month – the only blemish on his record to date.“Obviously we’re disappointed at times and so were disappointed with the result at Newcastle, so there’s feelings there,” he said.“It’s a sport, elite performance. You’ve got to play with emotion and feeling and sometimes that is a bit more aggressive, it’s a bit more intense sometimes, so you’ve got to manage that.“If I don’t manage that, you can’t expect the players to create the right emotion. So it’s certainly part of our role.”