The 28-year-old has not played competitively since previous manager Brendan Rodgers gave him time off to resolve personal issues in December.

But he has scored in all three of Celtic's pre-season friendlies.

"We're delighted not only in having him back but the contribution he's making as well," Lennon told Celtic TV.

Griffiths scored once in a 6-1 win over Austrian fourth-tier side Pinkafeld and a 2-1 defeat of third-tier Wiener before finding the net four times in a 9-1 bounce-game stroll against St Gallen Under-21s.

"No matter the opposition, to score quality goals like that shows that he's a quality player and a quality finisher," Lennon said.

"It's just pure instinct with him. He knows he needs to get a little bit fitter, but he's come a long way in a short space of time."

Lennon did not say whether Griffiths would be considered for Wednesday's Champions League first qualifying round first leg away to Sarajevo.

The manager, who also picked out Mikey Johnston for praise, revealed that fellow forward Vakoun Issouf Bayo is a possible injury doubt after also scoring against Wiener.

"We'll have to wait to see how he is," Lennon said. "He felt a little twinge in the hamstring - and he was looking really good as well."

Celtic return to Glasgow from their Austrian training camp to prepare for their trip to Bosnia-Herzegovina.

"I've got nothing but positive to say about the attitude of the players," Lennon added. "We know it's going to be difficult, we know the conditions might be difficult, the pitch might be difficult, the referee might be difficult and we have to prepare for all those things, but we know how crucial the game is for us now."