Manchester United manager Louis van Gaal has refused to rule out the possibility of signing goalkeeper Victor Valdes.
Manchester City boss Manuel Pellegrini says he is confident that England goalkeeper Joe Hart will sign a new contract.
Press Association Sport understands the 27-year-old Senegal international has rejected the club's latest offer as they attempt to negotiate out the release clause contained in his initial contract.
Despite concerted speculation during the summer, no potential suitor activated the £7.5million get-out which could have lured the former West Ham frontman away from St James' Park.
However, while supporters heaved a sigh of relief that last season's leading scorer would be staying on Tyneside, manager Alan Pardew revealed that the clause would become active once again next month.
The Magpies have been locked in negotiations with Ba's representatives for some time, but there is understood to be a significant gap between the wage deal the former are prepared to offer and that which the latter are willing to accept.
Newcastle are hopeful that the player, who has scored eight times to date this season, is happy to stay and he too has given little indication that he is looking to leave.
Pardew will hope for a breakthrough if he is to avoid a month of waiting anxiously to see if the former Hoffenheim player will remain within his grasp by the end of it.