Manchester United have rejected a world-record bid from Arsenal for England forward Alessia Russo.
The Euro 2022 winner, 23, turned down an offer to sign a contract extension at Manchester United in June.
Arsenal, three points behind Women's Super League leaders United with a game in hand, have been monitoring Russo's contract situation throughout January.
The bid was understood to be more than the £400,000 Barcelona paid for England midfielder Keira Walsh in September.
Russo's contract with the Red Devils runs out this summer and the deadline for domestic transfers in the WSL is 17:00 GMT on Tuesday.
Clubs are free to talk with Russo because she has fewer than six months remaining on her deal and, while United have continued negotiations with the player, no agreement has yet been reached.
Russo has scored 17 goals in 35 WSL appearances for United since joining from North Carolina Tar Heels three years ago, and netted 10 times in 17 games for England, including four in the Lionesses' Euro 2022 triumph last summer.
Manchester United have maintained they do not want to lose Russo, but with her contract expiring in the summer and talks over a new deal stagnating, they may find it hard to turn down significant offers.
Arsenal, who are also understood to have made an offer for Lyon's Danish striker Signe Bruun, have maintained their interest in Russo for several months and are certainly testing the waters.
It would take a huge sum to draw her away from United before the summer, but this initial offer shows the Gunners mean business.
Russo is one of the outstanding players in the WSL and her departure, should it happen, could drastically damage United's title challenge.
Arsenal themselves are in the title race and if they are able to persuade United to sell one of their major assets, it would further boost their chances of getting their hands on the trophy.
Russo has attracted interest from clubs in the United States and several top teams in Europe - including WSL rivals Chelsea - where she started her senior career - and European champions Lyon - and both could yet make a move before the deadline.
Should United choose not to sell, they risk losing Russo for free in six months.