Manchester United manager Jose Mourinho says the club face a tough campaign if they do not strengthen the squad before the transfer window shuts on Thursday at 5pm.

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.

Brazil international Fred, full-back Diogo Dalot and goalkeeper Lee Grant are the only new arrivals at Old Trafford this summer and the Portuguese manager has vented his frustrations at the lack of transfer activity.

There are also concerns over the future of Frenchman Anthony Martial, whose relationship with Mourinho has broken down, whilst the likes of Marcos Rojo and Chris Smalling are reportedly attracting interest from Wolverhampton Wanderers.

United kick off their season at home to Leicester City on Friday and the hosts are firm 1.44 favourites to pick up the win. The draw is priced at 4.20 and the Foxes are 7.50 outsiders.

Although the Red Devils are fancied to start off with a win, Mourinho has warned supporters to strap in for a bumpy ride if the club fails to bring in reinforcements.

He told MUTV ahead of his side’s pre-season friendly defeat to Bayern Munich on Sunday night: “My CEO knows what I want and I still have a few days to wait and see what happens.

“The other clubs who compete with us are really strong and already have fantastic teams. Or they are investing massively like Liverpool, who are buying everything and everybody.

“If we don’t make our team better it will be a difficult season for us.”