The U’s welcome Portsmouth in their Sky Bet Championship opener, and are without a handful of first team players.
Ciaron Brown is recovering from the knee ligament injury suffered at the end of last season, while summer signing Luke Harris and Ole Romeny both have ankle problems.
Placheta meanwhile has recently suffered a minor issue with his back, plus a tight hamstring.
The winger has though returned to training this week, and will be hoping to be involved in some way when United host Pompey.
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U’s head coach Gary Rowett said: “Shemmy has been training. We’ve got to assess where some of those players are. We’ve had some players that have played more minutes than others in pre-season.
“We’ve got some players that might only over the last two or three weeks have played 45 minutes in pre-season.
“It won’t necessarily be on paper this is what I think my strongest starting line-up XI is. This will be the most competitive starting XI I think is ready to attack the first game.
“If you’re one of those players, you get an opportunity to stay in the team. We’ve got that competition this year, we’ve got stronger competition this year.”
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Rowett added: “We’ve had some challenges. It’s probably been very unusual in terms of the amount of injuries that we’ve had over a period of time, but that’s what it is.
“I’m sure every manager of a Championship side this pre-season will say ‘we’ve had some injuries’.
“It’s not ideal. Everyone will say the same thing. You want every single one of your players available and the reality is that’s why you have a squad to cope with one or two of those.
“You hope it doesn’t come that early, but we’ll be ready to go on the pitch and start the game.
“We’ll be ready to make an impact. I’m sure we’ll be keen to do that in the first game. Pre-season is over. The real stuff now starts.
“Portsmouth had a good season themselves, a little bit similar to us last season. Home form was a big factor in that for them, home factor was a big factor for us.
“It’s a new season, it’s a new game. I don’t think either manager will read too much into the game from last season.
“It’s a fresh one, but for the first one, certainly we’re hoping to get off to a good start. That’s our focus. It’s in front of our fans and the emphasis is on us to go and make the running in the game.”