Radamel Falcao faces an anxious wait to find out the extent of the knee injury he sustained during Monaco's French Cup game against Chasselay.

Falcao, tipped to be a star for Colombia at this summer's World Cup in Brazil, opened the scoring in the 29th minute but was later caught by a heavy tackle from the Chasselay defender Soner Ertek.

The 27-year-old Falcao had turned neatly into the penalty area when he received a pass but, as he was about to line up a shot, Ertek came charging in from the side, all of his weight hitting Falcao's knee. No penalty was given, though Ertek was nowhere near to winning the ball.

Falcao was clearly in pain as he clutched his left knee and immediately called for medical attention.

The incident left his coach, Claudio Ranieri, complaining angrily that the match referee, Philippe Kalt, had ignored his requests to take firmer action against Chasselay's players. As Falcao was being taken away on a stretcher, Ranieri remonstrated furiously with Kalt, and could be heard screaming "I told you before."

After the game – which Monaco won 3-0 via two goals from Falcao's replacement Emmanuel Rivière – Ranieri explained that he felt his players had not been protected enough.

"I'm very satisfied [with the result], but I'm not happy with the referee. It's normal that the Chasselay players were tough, and that something could happen to someone. But there were no cards given. I hope that it's nothing serious for Falcao."

The Monaco captain, Jérémy Toulalan, told Eurosport: "We lost Radamel Falcao. It's a big blow. I think it is serious. The news is not reassuring."

Falcao, who had been linked with a possible move to Chelsea, is Colombia's key attacking player, having scored 20 goals in 51 international matches.