The England player damaged his eye socket when a ball smashed through his helmet grill, breaking his nose and injuring his cheekbone while batting against Northamptonshire.
The 27-year-old, who has already been ruled out of the 2015 county season, is due to undergo further assessment with a specialist in Belgium this week.
"We're hoping that after he sees the specialist he'll have a method of getting his eye back to 100 percent," Maynard told the BBC.
"The feedback we get from that will be quite instrumental but potentially it could be career-ending."
South Africa-born Kieswetter returned to non-international action in September after undergoing facial surgery.
While playing for the Warriors in a domestic Twenty20 competition in South Africa, he realised his vision was still impaired.
"He came back for a couple of games and although he knew the eye wasn't quite right, he was just delighted to be back playing at that stage," said Maynard.
"Then he went out to play in South Africa in the Twenty20 and he struggled. He was struggling to pick up the line and length of the ball.
"If you can't do that, it's going to be hard to score runs and it also makes you very vulnerable."
Kieswetter, who has played 46 ODIs and has an average of 30.11, was included in England's initial 30-man squad for next month's World Cup but later replaced by Sam Billings.
(Writing by Pritha Sarkar, editing by Tony Jimenez)
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