Celtic fear Gary Hooper could be out of action for some time after sufffering suspected ankle ligament damage against Kilmarnock.
The former Scunthorpe United marksman landed awkwardly in the first half of the 1-1 draw at Parkhead on Tuesday night with initial concerns he could have sustained a broken leg.
Hooper was stretchered from the field and Lennon is refusing to speculate on how long a period he could be out of action for.
The Bhoys boss is not yet ruling him out of the Old Firm clash against Rangers in the new year, although a scan on Wednesday morning should ascertain the severity of the injury.
"The early prognosis isn't good," said Lennon. "It looks like ankle ligament damage.
"It is too early to say whether he will miss the game against Rangers, I wouldn't like to call it. I watched it again on the television and it looks like he's stretched his ligaments.
"There's a worry about his fibula but we'll get a scan in the morning.
"It's a huge blow because he is our leading goalscorer and if he had stayed on the scoreline could have been different."