Jose Mourinho has warned Manchester United face a difficult season if they do not strengthen their squad before the transfer window shuts on Thursday. United's build-up to the new campaign has been dominated by Mourinho's clear frustration over transfers, which has brought his relationship with executive vice-chairman Ed Woodward into the spotlight.

The only arrivals into Old Trafford this summer have been Brazilian midfielder Fred, teenage full-back Diogo Dalot and back-up goalkeeper Lee Grant, leaving Mourinho to cast envious glances at how his rivals are shaping up for the new Premier League season.