Scotland winger Forrest, who remained on Pearce’s shortened list of contenders, missed the last two months of the season with a calf injury and Lennon says he will not be fit enough to go to the Games.
The 20-year-old has previously said he would rather play for Celtic in the Champions League qualifiers, which clash with the Olympic tournament in late July and early August.
Speaking to STV, Lennon said he did not expect to lose players for the tournament.
“Certainly not the British players, we’ve spoken with Stuart on that,” Lennon said.
“James Forrest will not be going because he’s been injured. Stuart’s aware of that.
“He was in his thoughts but the fact that he’s been out for so long probably rules him out.”
South Korea have said they plan to call up Celtic midfielder Ki Sung-yueng but the 23-year-old’s birthday falls weeks outside the deadline that would make his attendance compulsory under FIFA rules.
Lennon said: “As regards the rest of the players, we’ll speak to the other federations regarding that and hopefully there will be some sort of resolution where they are playing with Celtic when the time comes.”