TVN24, Poland, reported Walesa, a son of former Polish President Lech Walesa, was riding the motorcycle on National Road No. 10 Friday in Stropkowo in central Poland and collided with a Toyota RAV4.
He was flown by helicopter to a hospital in Plock, where he was in serious condition with injuries to multiple organs, medic Robert Galazkowski said.
Officers found Walesa, 34, nearly 100 feet from the accident site.
Walesa became a member of the Polish parliament in 2005 and has been a member of the European Union parliament since 2009, his Web site says.
He came to the United States in 1995 and graduated from Glastonbury High School in Connecticut and The College of the Holy Cross in Massachusetts with a bachelor's degree in political science.