Jose Mourinho is still looking to add further additions to his expensively assembled Manchester United squad this summer.Victor Lindelof and Romelu Lukaku have both arrived for a combined £105.7 million, but the Portuguese believes there is still plenty of opportunities for United to strengthen this summer.The United boss has already successfully brought in Wayne Rooney's replacement and reinforced his back line. But it's apparent the 54-year-old believes there is still more to be done.It's been a tough transfer window for most of the Premier League's top clubs, as player valuations continue to inflate - making it tougher for the likes of United and co. to sign their targets.Perhaps 12 months ago, Lukaku could, potentially, have arrived for nearer half the price; but his performances for Everton last campaign put the Toffees firmly in the driving seat to maximise their profits.And there are certainly no signs that the difficulties in the transfer market for Mourinho are set to ease up anytime soon, as clubs hold out to maximise their profits on players.

Mourinho targeting title charge

The difficulties facing the former Chelsea and Real Madrid boss are far from ideal for the man who is aiming to secure United's first Premier League title in the post-Alex Ferguson era.

Providing Manchester City complete the signings Benjamin Mendy and Danilo from AS Monaco and Real Madrid respectively, their summer spending will surpass the £200 million mark. 

However, at the current rate, it appears Mourinho will not be too far behind in the spending charts if he gets his way with the pursuit of Tottenham's Eric Dier. 

It's been no secret that the Red Devils have a firm interest in the England international who has significantly impressed since joining Spurs from Sporting Lisbon in 2014.

United make offer for Dier

And according to Sky Sports' Jim White, United have submitted a £40 million bid to the north London club for the 23-year-old's services.

Tottenham are desperate to keep ahold of players like Dier, alongside the likes of Harry Kane and Dele Alli, who the north Londoners wish to build their team around.

Mauricio Pochettino has proven to be a great success at White Hart Lane, and it's clear the Argentine has no intentions of continuing the club's development without them.

It's understood Dier would be interested in a switch to Old Trafford but, as of yet, it remains to be seen what the threshold is that will break Spurs' resistance.