Radamel Falcao scored just four league goals for Manchester United last season Getty

Former Chelsea striker Hernan Crespo says Radamel Falcao is no longer the same player he was before his serious knee injury.

Colombia international Falcao scored over 100 goals in his first three seasons in European football and was widely touted as one of the best strikers in the world, but suffered an anterior cruciate ligament injury at Monaco in January 2014 that sidelined him from the Brazil World Cup.

Falcao is hoping to resurrect his career at Chelsea after sealing a surprise loan switch to Stamford Bridge earlier this month, but Crespo has warned it will not be easy to impress the Blues boss Jose Mourinho.

"There is a big difference between Falcao before and after his injury," Crespo told BBC.

"Before the injury, he was the best of the 'human players' – all players apart from Lionel Messi and Cristiano Ronaldo, who are on another level.

"After such an injury, you need time and it's not easy to recover.

"It won't be easy for him. Jose doesn't give presents away," added the 40-year-old, who was loaned out to AC Milan during Mourinho's first season at Chelsea back in 2004.

The Colombian striker recovered after undergoing knee surgery and secured a high-profile loan move to Manchester United on deadline day last August, but failed to light up the Premier League, scoring just four times in 26 league appearances in the 2014/15 season.

Crespo says Falcao did not suit Louis van Gaal's style of play last campaign, but remains hopeful the South American will get a chance to shine under former Real Madrid manager Mourinho at Stamford Bridge.

"All Falcao has to do is believe in himself and be the great player he is. That will be enough to convince Mourinho to give him a chance," the former Blues striker said.

"He was probably not the kind of player [Manchester United manager Louis] Van Gaal was looking for. You have to take your chances if you want to play regularly. We will see what happens at Chelsea."