The former Manchester City player was again left out of Lambert's matchday 18 for Saturday's Premier League clash at Arsenal.
Ireland's last action was in the Capital One Cup semi-final with Bradford nearly a month ago. But Lambert reiterated that his decision is based on footballing reasons.
He said: "I have to pick as squad that I think will benefit the football club. He (Ireland) has featured up until recently.
"It is my decision. Stephen has got a contract, I've had chats with him and we get on well."
Lambert has a trio of injury concerns - including skipper Ron Vlaar - to contend with ahead of next Monday's home encounter with champions Manchester City.
Defender Vlaar was ruled out of the game at the Emirates Stadium with a calf injury along with club-record signing Darren Bent and experienced goalkeeper Shay Given.
Lambert said: "Ron got a knock on his calf, Darren got a kick on his foot and Shay has a little strain."
Stephen Ireland - the Villa enigma shrouded in a mystery. There is no doubt he has talent but has progressed way beyond the stage where 'potential' is sufficient in itself to merit a place in the starting 11 - as Delfonouso has become well aware along with Albrighton. The fact that he could be voted the fans player of the season merely reflects the collective amnesia of the claret and blue tinted fans who still inhabit a fantasy world based on - nothing. I believe Lamber claimed to get on well with Hutton and Warnock so Ireland should take careful note - doubtless, like Bent, he is happy to sit out his contract - no one else is going to be stupid enough to pay them these sort of wages - but don't expect to play too much.- timp