Atletico Madrid executive Clemente Villaverde predicted an "open group" after his side were drawn to play Benfica, Galatasaray and FC Astana in the Champions League group draw on Thursday.
Atletico have played both Portuguese champions Benfica and Turkish club Galatasaray in recent competition, however Champions League debutants Astana will be more of an unknown entity.
Speaking from the ceremony in Monaco, Villaverde told reporters the trips to Lisbon and Istanbul were sure to be difficult, and said there was lots of work ahead for Diego Simeone's side.
"It is a very competitive group," he said. "Benfica and Galatasaray are well known. At home they are very strong, so the group is open, and will give us a lot of work."
The draw means some long journeys for Atletico, especially the trip to central Asia to face Kazakh side Astana.
"The trip to Astana is a long journey, with four hours time difference, so the game will have to be played very late," Villaverde said. "They are a team that are in the draw, and we must play them. We must adapt and take it on."
Atletico were finalists in the competition in 2014, and were eliminated after two tight legs against Real Madrid in last season's quarterfinals. Villaverde said this summer's transfer business, with Atletico spending big on attackers Jackson Martinez, Luciano Vietto and Yannick Ferreira-Carrasco, should help the team to compete again.
"We work every year to improve what we have," he said. "Then the result can come with that or not. The work is there. If we want to retain our status, we must keep working like this. We have a good forward line, yes, but we must show that."
Villaverde also spoke about Argentine midfielder Matias Kranevitter and Colombian forward Rafael Santos Borre, suggesting moves for both youngsters were close to completion, but the issue of whether Kranevitter would stay with current club River Plate until January had yet to be settled.
"We are negotiating," he said. "Today [Kranevitter] passed his medical and we will [see] what we decide with River. We must respect them, and see what is best for both parties. He is a player for the future -- like Santos Borrre."