Grealish, 18, took to Twitter last week to announce that an agreement had been struck for him to remain with Shaun Derry's side for the remainder of the season.
However, the League One club were not able to get the deal over the line and the teenager has returned to Villa Park for talks over his future following the Magpies' 2-1 win over Sheffield United.
"We've made Jack the offer to stay until the end of the season and he wants to remain here," Derry told the Nottingham Post.
"The paperwork needs to be done and I would have liked it to have been completed yesterday if I am honest.
"As it stands though, he has to go back to Aston Villa to discuss what the future holds in the short term.
"I know what will happen long term - he will play first-team football for them. But he has numerous options at the moment.
"However, we do need answers quickly because we've put certain other players on the backburner.
"That isn't right for them and it isn't right for us and where we want to go."
Grealish has made 19 appearances in all competitions for the Magpies, scoring three goals - the last of which came in a 3-0 home league win over Bradford on New Year's Day.
The Magpies are also looking to extend Callum McGregor's loan from Celtic, which expired at the start of the month.
However, other clubs are interested in the midfielder - with Wolves thought to have made a bid - and the Scottish champions have yet to make a decision on the 20-year-old's future.