Walcott, 23, rejected an improved contract offer with the Emirates club while the Gunners last negotiated any deal way back in August. Such circumstances have paved the way for Premier League giants like Liverpool, Chelsea and Manchester City to bid for the England international.
Arsenal put forward a contract worth £75,000-a-week for five years but Walcott turned down the offer demanding a deal closer to £100k weekly.
Several clubs are interested in Walcott, who has only six months left on his current deal, but the prospect of joining the league leaders could tempt the winger.
Meanwhile, United have more chances to land Walcott as Arsenal is exploring a January swoop for United misfit, creating a chance for a swap deal between the two clubs.
Walcott could be available for a cut-price £8 million and the Reds boss Brendan Rodgers is looking to bid but Liverpool are closing on signing Chelsea forward Daniel Sturridge and Tom Ince.
United and Arsenal are also eyeing a move for Crystal Palace winger Wilfried Zaha.