RIO DE JANEIRO, Aug. 26 (Xinhua) -- Fluminense striker Pedro is a doubt for Brazil's friendlies against the United States and El Salvador due to a knee injury.

The 21-year-old was forced off at halftime of Fluminense's defeat to Cruzeiro in Brazil's Serie A championship on Saturday after twisting his right knee.

Tests on Sunday revealed the center-forward strained ligaments and will need at least two or three weeks to recover, according to newspaper O Globo.

Pedro is the leading scorer in Brazil's top flight this season with 10 goals in 19 matches. He has netted 19 times in 41 appearances for Fluminense across all competitions this year.

The No. 9 was this month rewarded for his impressive form by earning a maiden call-up to Brazil's national team for friendlies in the United States.

The five-time world cup winners face the United States in New Jersey on Sept. 7 and El Salvador in Washington four days later.