The Harlequins back was knocked out early in the first-half of England's victory over Italy at Twickenham on Feb. 14 and suffered a setback in his return-to-play protocol.
Lancaster said news on Brown was "very encouraging" and he was on course to return to full training on Friday.
Brown was replaced by Alex Goode against Ireland with the Saracens man producing an impressive overall performance, despite being beaten in the air by Ireland's Robbie Henshaw for the game's only try.
Unbeaten Ireland's third victory of the tournament has left the holders in pole position to retain their title but Lancaster said England, who have home games left against Scotland and France, were still in the mix.
"This time last year Ireland were probably sat in the same position as we are this week having lost against us in the third game and obviously two weeks later they have a championship medal around their necks," Lancaster told Sky Sports.
"We do rely on other results. You never know, Ireland have got to go to Wales... Wales have got huge motivation.
"They could still win the championship if they beat Ireland and Ireland have still got to go to Scotland as well."
Ireland take on Wales in Cardiff in the next round of games with the Welsh back in confident mood after a following up victory over Scotland at Murrayfield with a 20-13 win over France on Saturday.
Wales, beaten by England in their opening game, sit third in the standings behind Lancaster's side on points difference.
England have a points difference of +25 compared to Ireland's +40, a factor that could come into play by the end of the tournament with England's last-minute disallowed try for winger Jack Nowell against the Irish becoming a potentially pivotal moment.
(Reporting by Justin Palmer, editing by Pritha Sarkar)
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