The Gabon international, who remained at Southampton during the international break as he recovers from an ankle injury, wrote his tribute to the veteran shot-stopper on Instagram after watching Buffon's tearful speech at the end of Italy's goalless World Cup play-off draw against Sweden on Monday.
The result means Italy haven't qualified for the 2018 World Cup - the first finals the nation will miss since 1958 - and brought forward Buffon's international retirement.
But Lemina, a team-mate of Buffon's at Juventus until last summer, suggested the keeper should be proud of his achievements for the Azzurri.
"You've done so much for Italian football," he wrote. "You are a monument to us... thank you for everything. It was an honour to play with you. Great Gigi. But you still have Serie A and the Champions League to win."