Manchester United may have signed Victor Lindelof and Romelu Lukaku for a combined £105 million so far this summer, but Jose Mourinho still isn't happy.

Speaking to ESPN earlier this week, the Portuguese expressed frustration at how he's struggling to hit his target of four major signings.

"We always feel there is room to improve, and I cannot say that I am happy with our transfer window," he said, per Manchester Evening News.

"What I can also say is that it is a difficult transfer window and I don't blame anyone - it is just a reality of things. The market is going in such a direction that many players are difficult to get, not to say impossible."

Ivan Perisic, Nemanja Matic, Eric Dier, Alvaro Morata and Fabinho have all been linked with United in the transfer window but, for one reason or another, deals for all five have fallen through.

Only Morata's future has been decided of the five, though, meaning United could yet sign the remaining four.

It's Tottenham midfielder Dier that Mourinho seems to want most, after the Mirror reported on Monday that he's willing to spend up to £60 million.

Spurs, however, are having none of United's advances and insist the England international isn't for sale at any price.

Chairman Daniel Levy and manager Mauricio Pochettino have already given the green light to Kyle Walker joining Manchester City for £50 million and don't want to lose another first teamer.

What could influence a potential move, though, is how Dier feels about United's interest and Tottenham's refusal to sell.

According to Manchester Evening News' Samuel Luckhurst (see below), Dier is 'desperate' to join the Red Devils this summer.

Tottenham may have finished second in the Premier League last season, four places above United, but clearly the prospect of playing for England's biggest club excites Dier.

His desperation to join Mourinho's side presents a big problem for Pochettino, who hasn't signed a single player so far this summer.

Quite why that's the case is unknown, but the Argentine must realise that time is of the essence given the new season starts in just over three weeks.

Lose Dier and Pochettino would have yet another large void to fill - far from ideal when Tottenham's rivals are all signing world-class players.