Former Manchester United manager Sir Alex Ferguson thinks the Red Devils' summer spending is "amazing."

After appointing Louis van Gaal earlier in the summer as David Moyes' successor at Old Trafford, the 20-time English champions have strengthened their squad in order to return to the Champions League and challenge for the title.

United have signed Ander Herrera, Luke Shaw, Marcos Rojo, Angel Di Maria, Daley Blind and Radamel Falcao. The Argentine winger arrived at Old Trafford in August from Real Madrid for a British record fee of £59.7m.

The Red Devils have spent over £150m during the summer transfer window. Ferguson enjoyed great success at United as the club's manager. The Scot who retired from his post in May 2013 says he is fortunate in not being involved in transfers any more.

"Certainly it's amazing, the amount of money spent nowadays. Fortunately, I'm not at the hub of it nowadays," the Mirror quoted Ferguson as saying.

"My personal opinion is that it's never going to change, the world is progressing, and transfer fees with it, and I don't know if there will be an end to it," United's legendary manager added.

Meanwhile, one summer signing Rojo was ineligible to play for United against Sunderland and Burnley as he did not have a work permit. However, the Argentine international was granted a UK visa on Thursday.

The versatile defender arrived at Old Trafford from Sporting Lisbon and is in contention to make his United debut, along with Blind and Falcao against Queens Park Rangers on 14 September. Rojo says he is eagerly awaiting his debut for the Red Devils.

"I am desperate to get onto the field and play because I have not been able to step onto Old Trafford [yet]," Rojo explained.

"My life has changed a lot. I am very happy to be at Manchester United, a top team in the world, sharing a dressing room with players like Wayne Rooney, Robin Van Persie, Angel Di Maria and now Radamel Falcao."

"This is a very important step in my career as a player and as a person. Everything that has happened to me since the World Cup has been a dream," the Argentine added.