The Scottish champions beat McGeady's Spartak 2-1 at home on Wednesday night to qualify for the knockout stage of the Champions League and the Irishman was thrilled to see some of his old teammates come together under the manager that took over just before he departed for a fee of £9million.
"The team now probably play for each other a bit more," he said.
"When I left we were in a bit of a transitional phase after Tony Mowbray had gone and Lenny took over.
"Lenny has done a great job. With the resources he has, to qualify for the last 16, to go through two qualifying phases as well, you take your hat off to him and to the players."
McGeady did not agree with some critics that Celtic were lucky to get through, suggesting their performances spoke for themselves in finalising progression.
"I'm not 100 per cent sure about that. Any team that has ten points deserves to qualify but at times Celtic have been lucky. When they beat Barcelona they rode their luck a little bit but, overall, they deserved to go through," he added.
"Now it's all about the luck of the draw. They could get a really, really top team in the next round - but then they beat Barcelona here so they can do anything.
"With the crowd and that great home record - even stretching back to when I was here - anything can happen.
"The players will just be buzzing that they have made the last 16."