Celtic had a free weekend after going out to Aberdeen in the fifth round of the Scottish Cup but when the squad reported back to Lennoxtown at the beginning of the week, both Biton and Forrest were carrying groin problems.
"Nir and James both went for groin scans on Monday and we think Nir is going to be a bit longer-term than Jamesy, and we will need to wait and see what results the scans brings back," the manager told the Celtic View ahead of Friday night's Scottish Premiership trip to Kilmarnock.
"I saw a bit of the England v Denmark game as I was down there and unfortunately Fraser didn't get on and then I watched a bit of Ireland and Stokesy never got on either!
"But really what you do is sit around and wait and hope the news is good and they have come back in good condition and, bar the two, they are in good fettle and good form."
However, following his stunning winning goal for Scotland against Poland, Lennon admitted there was a spring in the step for captain Scott Brown.
"That's the flip side of it," said the Hoops boss. "Guys go away with their country, and they are delighted to go away, and then they get a positive result and come back feeling good about themselves.
"We do have a lot of international players here at the club, and (Emilio Izaguirre's) Honduras had a good win as well.
"There are peaks and troughs with them but they came in on Monday and they looked really bright, and the weekend off will have done them the world of good as well."
Those who were fully fit and were not called up by their countries were given an extended break to recharge their batteries.
"We do that with the majority of them who aren't away with their countries - Virgil (van Dijk), Derk (Boerrigter), Krissy Commons - they come and do a bit of physical work and then have a bit of rest," added the Irishman.
"I also went away for the weekend back home, so I got home to see my parents which was lovely."