Johannes Hoff Thorup has confirmed that Lucien Mahovo has suffered a setback in his recovery from injury and will remain unavailable.
The young full-back has been absent since the win against Stoke City with a knee problem but has now suffered a second injury during his recovery.
Unfortunately, he felt something in his quad and could not continue in training. He'll be out for a while," the Dane said.
"Originally, it was the knee, this is another injury."
Matěj Jurásek was left out of the matchday squad at Home Park but isn't expected to be out for too long while Liam Gibbs is close to a return.
"Still feeling some pain, we have to be more patient (with Matěj) and more careful with how we treat him," Hoff Thorup explained.
"I would love to bring him in and to give him some minutes, some experience, playing time with the team. I want him to feel the stadium as a starter before the end of the season.
"(Liam) is in a good place, he'll be around the squad tomorrow. He's more around the squad to give us extra support, we're low on numbers again. There'll be some 21s players again, we only have 15 or 16 first-team players.
"I want to be as honest as possible but there are players we need to wait and see on tomorrow."
While discussing the club's current run of form, the City head coach pointed out that the squad and staff are accepting responsibility as a group.
They suffered a 2-1 defeat to Argyle on Saturday.
"I was not satisfied with it, watching it back I was even less satisfied with the situations. We'll do everything we can to fix it. It's a lot of the same situations we concede goals from, but it's also one of the most difficult things to train," he said.
"I try to be careful in what I say. Sometimes, it sounds like I'm blaming coaching staff or players. Set-pieces have been an issue, but it's not on one single coach to solve a problem. It's also the players, we haven't been good enough at set-pieces. We need some output."
With summer just around the corner, the topic of transfers was also approached with Jacob Wright's future a talking point.
The loan signing from Manchester City is available in the summer.
"We have a situation where a coach likes a player, a player likes a club. It's a discussion for the end of the season. We don't deal with contract situations based on one performance. He's in a good place, he's a great player.
"I think I'm aware now of who we can extend with or who will leave if they find somewhere else.
"We're not changing the strategy. Let's say if we sign 10 players, seven or eight would be high potential players but two or three would be experienced and ready to play a leadership role in the team.
"We lost to a team that had 100 passes at the weekend. That's part of the beauty of this league. We will look at the Championship that are available for us and would like to be a part of the way we are doing things."
Ahead of the visit of Sunderland, Hoff Thorup also pointed out the success of Sunderland's season.
They are almost certain of a play-off spot with a chance of automatic promotion still available, but also maintains that the reverse fixture at the Stadium of Light shows that City will challenge them.
"Well done to them. They've done a great job, it takes a lot. They've been up there since the start of the season. It's definitely something we can look at and take some learning from.
"They haven't just been below that group of best teams in the league, they've competed with them.
"We did well in what was a game without too many chances. We scored a good goal from a corner-kick but then concede from two free-kick situations, one immediately after a red card for José Córdoba.
"There's positives, the result wasn't one, but there are things we can bring to tomorrow's game.
"Nothing tells me that we can't go and compete with these teams, they'll be on top at times and so will we. It comes down to who takes their chances better. We can have a good performance and win, the same on Friday night."