Jansen joined Bolton in January after leaving Blackburn

However, Bolton hope to agree a new contract with Ivan Campo and Hidetoshi Nakata, whose loan deal from Fiorentina has ended, may return permanently.

"We need six quality players to bolster our squad for the coming season," boss Sam Allardyce told the club website.

"I want to bring in the majority of them before the World Cup starts."

Jansen, 28, joined Bolton on a short-term deal after leaving Blackburn in January.

Fadiga, 31, was signed by Bolton in 2004 after a spell at Inter Milan, while Perez, 24, arrived on a free transfer last January after being released by Cordoba.

Bolton had their first taste of European football this season but after a promising start the season fizzled out and they finished eighth in the Premiership.

Top of Allardyce's wish list is a new striker but finding a replacement for influential defender N'Gotty will also be a priority.

"I've scoured the globe to bring in the right quality we need," he added.

"It is a difficult and delicate process but one that I will relish as we aim to continue our progress in the top flight of English football."