The 27-year-old hit out at an account attributed to Lewisham Athletic FC on the social media platform which accused him of lacking loyalty, amongst other things, after his absence for the Championship encounter at The Den.
Wallace has been linked with a move away from the Lions this month as he enters the final six months of his contract.
Forest, Middlesbrough and Turkish giants Besiktas have reportedly all had offers rebuffed by Millwall during the current transfer window, while Premier League duo Watford and Leeds are also apparently keen.
The forward hasn’t featured for the south London side since December 11 because of a quad injury.
He was expected to return for Saturday’s home against Steve Cooper’s side but suffered an injury setback in training on Friday which prevented him from being involved.
Millwall boss Gary Rowett confirmed the injury update after his side went down to a 1-0 defeat against Forest.
He said: ‘He (Jed) had a little quad strain. He trained Tuesday and Thursday and just felt his quad Friday.
‘He’s had it scanned. I don’t think it’s particularly serious but there’s something there to concern him.’
Now, Wallace has felt the need to explain his absence himself after being provoked on Twitter.
Responding to the claim, the former fans’ favourite at Fratton Park tweeted: ‘Thank you for your kind words, I’ve played over 200 games for Millwall & never took that for granted.
‘Would never ever refuse to play, I’ve just had a minor setback on my injury.
I’m not a robot these things happen and I’m doing all I can to get back to playing ASAP. Thankyou.’
Forest remain the favourites to land Wallace, who scored 30 goals in 111 outings for Pompey during a three-and-a-half-year stay at Fratton Park.
The player retains strong links with the Blues and gave the club a ringing endorsement ahead of Mahlon Romeo’s loan switch in the summer.