Celtic opened the competition with a 2-1 win over Club Brugge at 10.30am then followed that up with a 4-1 win over KAA Gent early in the afternoon.
“It’s great to get off to a winning start,” the former Hearts boss said. “These competitions are very strong and competitive so two wins is very satisfying.
“The players have settled quickly and are looking fit and sharp. A lot of the credit for that is down to Ian Call our sports scientist. He’s designed the fitness work and it’s paid off.
“It’s still all about fitness for us at this stage but obviously it’s pleasing to be getting some good performances and results as well.
“We’ve came over here after three games against strong English opponents and are reaping the benefits of those matches.
Frail added: “I was pleased with the performance against Brugge, they made it hard for us but we kept up a good tempo and came through strongly.
“Jordan Lowden scored a great solo goal from midfield then Patrik Twardzik finished off a good move then we got a bit sloppy and lost a late goal but held on for the win.
“In the second match we knew that Gent would be strong because we watched them against Eintract Frankfurt and although they lost 2-1 they played well.
“I was really pleased with our performance against Gent, the players really took to the game and showed up strongly to go four up.“Callum McGregor opened the scoring cutting in from the wing and finding the net then he set up James Keatings for the second.
“Their keeper parried a shot from Michael Ordish with Curtis Jones scoring from the rebound then Paul George scored with a great volley.
“We lost a late goal but the boys can be very pleased with themselves. We’ve a tough match with Botofogo to start tomorrow, they’ve won both of their games as well and have looked impressive.
“We’re in a good position but you can’t get complacent. These tournaments are very competitive, we’ve set high standards and need to continue them tomorrow.”
Brondby and Spurs are sitting at the top of Group B after winning both matches. The group stages will be completed tomorrow with Sunday starting with the semi-finals at 11am with the final starting at 4.30pm local time.