The Norwegian international scored seven and laid on six for his team-mates in just 13 appearances for the Hoops but barring an anonymous 45 minutes against Rangers in the Betfred Cup final, hasn't featured since 10 November.
Speaking ahead of Wednesday's trip to the Capital, - in which a win would take Celtic five points clear at the top of the Ladbrokes Premiership - Lennon admitted the 25-year-old could be sidelined for a while longer.
“He may be out for a little bit longer. It’s going to take a bit of time to settle it down," the Hoops boss told CelticTV, adding: "Ryan Christie is fit, we just had to manage him over the past few days. Jonny Hayes trained [on Monday], Mikey Johnston we're hoping is fit for, if not Wednesday, then definitely Saturday.
January transfer plans
Despite several players being linked with Celtic, including goalkeeper Joe Walsh of Gillingham, AEK Athens 'keeper Vasilis Barkas and Panathinaikos midfielder Giannis Bouzoukis, Lennon insists that there are no concrete targets for next month's transfer window.
He added: "We've got a meeting [on December 17] where we'll sit down and discuss things, discuss options and we'll hopefully pinpoint one or two players and try to get a move on with that, but nothing at the minute."
'Frimpong... could play left-back'
Lennon also spoke about the meteoric rise of young right-back Jeremie Frimpong, praising his contribution since he broke into the Celtic first team - but doesn't see him playing further forward as a winger, for instance.
"He's done exceptionally well [at right-back]. We've played him at wing-back once or twice and he's still getting to know the role, but that position seems to suit him as well," he said.
"He is that good that he could comfortably play left back as well, I think, with what he has in terms of his attributes - his pace, reading of the game - but at the minute we see him as a full-back."