Jenas, signed on loan from Tottenham in the summer, has caught the eye with his enthusiasm since arriving in the West Midlands.
However, Grant fears he is in danger of going to extremes in a bid to impress, illustrated by him currently out for three weeks with the heel problem.
He told the club's website: "Of course we have got a break now for the internationals and we hope that will help speed up his recovery.
"He is in very good hands here with the physios and the doctor and we are delighted that he seems to be responding quickly.
"We have seen it before where boys are desperate to play and try to rush themselves to get fit - more so in Jermaine's case because the supporters haven't seen him yet."
Source: Team Talk