Voges was struck on the back of the head by a ball lobbed by sub fielder Ollie Rayner and missed by wicketkeeper John Simpson after a boundary hit by Hampshire’s Michael Carberry at Southampton.
The 36-year-old fell straight to the floor before being helped off the pitch by two physios and was subsequently taken to hospital with a suspected concussion as his participation in the game looks to have ended.
Middlesex director of cricket Angus Fraser said: “The feeling from the physio Peter Waxman is that it is a concussion but that will be shown up later.
“It was a freak injury but you wonder why when a cricket ball which gets thrown around the field as much as it does it doesn’t happen as often. A cricket ball is a hard thing.
“It is sad for Adam and disappointing for us as we will have no more use out of him in this match.
“He wasn’t feeling very well in the dressing room so we decided to get him to the hospital to get him checked over. He wants to remain here even if he can’t play.”