The 25-year-old defender suffered a head injury in Wednesday night's 3-1 EFL Cup defeat at Luton Town.
The 25-year-old centre-back was forced off at half-time of Wednesday night’s 3-1 EFL Cup first-round defeat at Luton Town after taking a knock to his head and will need to be assessed before the Villa Park opener.
Several players are also still short of match fitness after missing the majority of preseason with minor issues, but there are otherwise no concerns for Di Matteo’s squad.
Speaking about Baker’s status, the Villa boss told reporters: “We still have to assess him today. He got a knock on his head and we had to take him off, so we’ll see how he is today and we’ll make a decision.
“So far it’s only him and the rest of the group is ok.”
The 27-year-old defender, who started every game of Wales’ fairytale run to the Euro 2016 semi-finals, officially joined Villa from Midlands neighbours West Bromwich Albion on Friday afternoon on a four-year deal and is projected to be captain Tommy Elphick’s first-choice centre-back partner going forward.
However, the paperwork for his move is not believed to have been completed in time to be registered for the weekend [h/t Birmingham Mail], meaning that Baker's potential absence could see either Micah Richards or Jores Okore called on to start instead.
Update: Villa chief executive Keith Wyness has confirmed via Twitter that Chester's registration was completed one minute before the official deadline. Whether Di Matteo will throw him straight into the mix without a training session, though, remains to be seen.
"Obviously we’re now focusing on the game against Rotherham and the best recipe for everyone is winning the first home game," Di Matteo added at his press conference. "I think that would give the whole environment a big lift.
"I can see improvement in the team from the first day I came in. The team is changing – not constantly, but there are a few changes happening and I can see that we’re moving in the right direction. In the end, what you need is to have a good game, get a good result and that gives everyone the confidence going forward."