The phrase "probably concerned about" is correct and can be used in written English
It is typically used to express someone's likely worry or anxiety about something. Example: Sarah was probably concerned about her upcoming presentation, as it was her first time presenting to the whole company.
What she is probably concerned about is why our politicians have been ignoring her for so long.
But when Mr. Allawi proposed an amnesty for insurgents -- a move that was obviously calculated to show that he wasn't an American puppet -- American officials, probably concerned about how it would look at home, stepped in to insist that insurgents who have killed Americans be excluded.
Now, you're probably concerned about where we're gonna send all these fine downtrodden folks.
After taxiing, when it became evident that they would be delayed for a prolonged period, conversations between the crew showed that they were aware of and probably concerned about the risk of reaccumulating frozen contamination on the wing.
This discrepancy between 14 and 16 was unexpected: "I guess the thing that I was probably concerned about was um… observing something that I didn't expect and not being about to explain it immediately".
The documentary also spends far too much time examining Mr. Markopolos's paranoia (though if you were the only named complainant in a case involving billions, you'd probably be concerned about reprisals).
He spent the next 10 minutes carefully watching the burger in the pan, probably mildly concerned about not breaking the thing in half when he had to turn it over.
So using that logic, early-adopting customers and investors should probably be concerned about bugs later this year when Intel introduces two completely new microprocessor platforms: one for servers and one for desktops.
Marketers, especially those who focus on Social Media, are probably not concerned about the valuation of shares or the computer problems at NASDAQ.
"I would probably be concerned about losing the things that make me who I am".
They're probably not concerned about keeping their elbows tucked.
