HITC Sport understands from sources close to the club that Fulham have launched a raid on local rivals Brentford by making a move for defender James Tarkowski.
Tarkowski has impressed at Brentford since joining the club from Oldham Athletic in January 2014.
The powerful centre-back helped the club to win promotion from League One in his debut campaign and he was instrumental in the club's push to reach the Championship play-off semi-finals last season.
Fulham have made defensive reinforcements one of their top priorities this summer as they look to shore up a defence which was the second worst in the Championship last season, conceding 83 goals.
The Whites are believed to have made bids for the likes of Wolves' Richard Stearman, Brighton's Lewis Dunk and Sheffield Wednesday's Tom Lees, but have seen all their offers rejected so far.
As a result, Fulham have switched their attention to Tarkowski and are understood to have tabled a bid in the region of £2.25 million for the 22-year-old.
Brentford are reluctant to lose Takowski, but they could find it hard to turn down a sizeable offer for the centre-back.