Jose Mourinho has expressed his shock at the retirement of his 'best friend' Frank Lampard.

The former Chelsea star announced his decision to hang up his boots on Thursday.

And Mourinho, Lampard's manager twice during a trophy-laden career at Stamford Bridge, had not picked up the news when questioned ahead of his Manchester United side's trip to Leicester City.

Manchester United boss Jose Mourinho admits he didn't know Frank Lampard had retired

Lampard announced his retirement on Thursday following a spell at MLS side New York City

'He retired?' the Portuguese asked when informed of Lampard's decision. 'I did not know this.'

Mourinho added that while he was sad to see the 38-year-old quit, he was sure that he would enjoy a bright future off the field.

'I am really sad,' he said. 'It's the reality of life but I am really sad. I rate him one of my best players, one of my best friends in the game.

Lampard won a number of titles under Jose Mourinho during his time with Chelsea

'It doesn't matter what he chooses for the rest of his life he is going to be successful.

'I don't know what he wants but it doesn't matter. The direction he gives to his life, he will succeed. 'Best player, best friend. Top, top player.'