Figures released by retailer UKSoccershop.com showed that supporters have been snapping up more Lallana tops than any others in Roy Hodgson's squad.
The 26-year-old is narrowly ahead of captain Steven Gerrard, as well as traditional big names such as Wayne Rooney and Frank Lampard.
UKSoccershop managing director Simon Pretswell said: "The sales figures are a real show of support by the England fans for Lallana, with many backing him to feature in Roy Hodgson's lineup against Italy on Saturday.
"In previous tournaments, it has been the likes of Rooney, Gerrard and David Beckham who have occupied the top seller slot, so it is an impressive accomplishment for Lallana to be leading our figures.
"While it would be fair to say that Southampton fans are backing their captain, we are also receiving a number of international orders from customers around the world."