Clarke has missed City's last three matches after picking up a hamstring injury in the recent Barnsley game but Parkinson says the Irishman could now return to his match-day eighteen for Southend's visit to the Coral Windows Stadium.
Parkinson confirmed: "Billy Clarke is back in contention.
"He has trained for the last three days now, and that is another huge boost for us.
"Now that he is back, he comes straight into our thoughts for Tuesday's squad."
Although Clarke isn't expected to feature from the start against Southend on Tuesday night, Parkinson has hinted that he still could be open to change when it comes to his starting line up for the home match.
Parkinson added: "We have no new injuries from the weekend. All of the lads who didn't start on Saturday have trained well and that has left us with some thinking to do ahead of Tuesday evening.
"The competition we have for places, especially up top, is pushing players onto another level.
"Jamie (Proctor) played well and scored recently at Port Vale, (Steven) Davies has two goals in three games and (James) Hans has performed superbly on Saturday at Peterborough United.
"We have to pick a team which is fresh enough to go again this Tuesday.
"We do have some nice selection problems going into the match."