Whittingham, 25, has already been the subject of a failed bid by Burnley.
Cardiff chief executive Gethin Jenkins has started talks with Whittingham over a three-year deal as he will be out of contract at the end of the season.
Losing such a key player would be a massive blow to the cash-strapped Bluebirds who are currently unable to bring in a replacement due to a transfer embargo that is in place.
Former England under-21 international Whittingham, who signed for a cut-price £250,000 from Premier League side Aston Villa in January 2007, is attracting attention due to his goal-scoring record last season.
He also hit the woodwork nine times and chipped in with 10 assists to help make Cardiff the fourth top scorers in the Championship.
Source: BBC Sport
Source: BBC Sport