Whelan is reluctant to lose N'Zogbia, who he rates as the best left-winger in the Premier League, but is prepared to do business at £10million.
"It's £10m or there is no deal," Whelan told the Daily Mirror. "They offered us £9m and we refused it; firstly because we would like to keep Charles, and secondly because if he is to go, then we have to get the right price for him.
"Charles has played fantastically well in the last year and, with his pace and penetration, there's no doubt in my mind that he is the finest left-winger in the Premier League.
"We owe him a lot, not least for his goal against West Ham that helped us stay up.
"If the right offer comes in, we would consider it, if it was in his best interests - but it has to be the right offer."