Winston Reid
Winston Reid looks set to leave West Ham either in January or in the summerGetty Images

Arsenal must act decisively in January if they have designs on signing West Ham United defender Winston Reid before rival clubs hijack a potential deal at the end of the season.

Reid is out of contract in the summer and Hammers boss Sam Allardyce is consigned to losing the New Zealand international, with the Gunners and Manchester United both linked with the centre-back.

Though 17-year-old midfielder Krystian Bielik became Arsenal's first addition of the January window earlier this week when he joined from Legia Warsaw, a new defender is expected to arrive this month.

Villarreal's Gabriel Paulista is a confirmed target for Arsenal but the club may struggle to complete the deal because the Brazil defender does not automatically qualify for a work permit under the current regulations.

That stumbling block may force the club to look elsewhere, with Reid - who is valued at £3m in this January window - among the potential targets and Martin Keown says Arsenal must move fast or face losing him to a Premier League rival.

"Unless Winston Reid is prepared to leave now, I'm not sure they will [sign him]," Keown told The Daily Mail. "I think Arsenal want to sign somebody in this window and he may not be available.

"He's certainly improved since I first saw him and he's a good player now, though I don't think there's a big difference between him and James Tomkins.

"If they didn't think Tomkins was good enough, will they go for Reid? If they do, he will have to come in and play.

"Arsene Wenger expects all his players to be able to play. But right now, unless he's available, I don't think it will happen. I'm not even sure if the player would want to leave as he will be looking for guaranteed first-team football and I'm not sure he would get that at Arsenal."