Tomkins, 23, has been a long-term target for Newcastle manager Alan Pardew, who may have to replace captain Fabricio Coloccini because he wants to leave Tyneside and return to his native Argentina.
Sam Allardyce: “We have never been in a position to sell anybody and we don't want to.
“We want to increase the size of the squad, not decrease it.
“You never know what happens in this window because, if someone offers you an unbelievable amount of money for one of your players then the owners look at that and say that is too much to turn down - not that that has happened at the moment.
“But the most important thing for me is players coming in, not going out.
"We only have two centre-halves left, James [Collins] and [Winston] Reidy, and we have a young 19-year-old at full-back because we have no one else, so I need two if I am really honest.”