The Cottagers have had a bid for Cook rejected by the Rs, who rate their star man in the £3million bracket.
Sanchez is wary about spending that sort of fee on an unproven Premier League player - and will put a bid on the table at the Madejksi Stadium for South Korean ace Seol if the Rs refuse to budge on their valuation.
The 28-year-old played a starring role in the Royals' first campaign in the top flight last season and scored four goals in 26 appearances.
He cost £1.5million when he signed from Wolves in July 2006 - and Steve Coppell would be looking to make a profit if he were to sell him so is likely to value him at around £2.5million.
Sanchez would be happier paying that kind of money for a proven top-flight player, and will make a move if the Cook trail goes cold.