Roger Federer was vulnerable after break from the sport says Barry Cowan

Roger Federer's lack of match sharpness was exposed during his defeat by Albert Ramos-Vinolas at the Shanghai Masters, says Barry Cowan.

The defending champion was forced to relinquish the title in his first match at the China tournament after suffering a shock 7-6 2-6 6-3 to the Spaniard in the second round.

Federer, who was handed a first-round bye, had been absent from the ATP Tour since losing last month's US Open final to Novak Djokovic and showed signs of rust, making 30 unforced errors. 

Sky Sports expert Cowan believes the world No 3 has struggled in the past to regain his best form after a spell away from the sport, but also gave credit to Ramos-Vinolas for his unwavering composure in the deciding set.

"Every player is vulnerable first match when they haven't played for a few weeks, which is certainly the case for Roger. We saw that last year," said Cowan.

"Given everything into account, the fact he hadn't beaten a top 10 player, it's clear that clay or slower hard court surface are Ramos-Vinolas' best surface. But the longer you can hang in there in a set, the more potential there is for an upset to happen.

Every player is vulnerable first match when they haven't played for a few weeks, which is certainly the case for Roger. We saw that last year.

"He hadn't even created a break point let alone been able to break Federer's serve until that 4-3 game right at the end. He didn't blink did he?

"I thought Federer would strike back in that last game, but he held his nerve.

"I thought it was a stunning third set. It wasn't a case that Roger lost that third set, it was certainly the case that Ramos-Vinolas earnt it."