Celtic boss Ronny Deila says keeping his best players will take priority over acquisitions in the transfer window.
Chelsea striker Fernando Torres is understood to be set for a return to Atletico Madrid, according to Sky sources.
Norwegian midfielder Stefan Johansen is relishing the pressure of playing for "one of the biggest clubs in Europe" after completing his move to Celtic.
The international signed a three-and-a-half-year contract after Celtic tied up his transfer from Stromsgodset, last year's Norwegian title winners.
The 23-year-old admitted the move was a major step-up in his career but he did not appear to be the type of player to be overawed by expectations as he was introduced to the media at Celtic Park.
"Football is all about pressure," Johansen said. "You should always have pressure on you. We need to do our best in every match.
"Of course Celtic is a much bigger club than what you get in Norway but you get a little bit of the same from the press. The crowd should expect something from me, the media should expect something, the team-mates, but the biggest pressure I put is on myself.
"I improved a lot last season, 2012 was a good year for me but last season I had pressure on me. The fans and media were expecting something from me and I needed to prove I was capable of doing the same season again.
"We won the title and I made my debut in the national team, so it was a fantastic season and I really hope to continue. I'm going to work even harder here."
Johansen, whose switch is reported to be worth about £1.7million, added: "It's a big step. The league is better but the clubs in Norway are not even close to Celtic. It's a fantastic club.
"Celtic is one of the biggest clubs in Europe so I'm very happy to be here. You see how much the club means to the supporters so I'm looking forward to playing in front of them. They are probably the best fans in the world and the club is huge."
Some of Neil Lennon's summer signings have struggled to adapt to Scottish football, notably forwards Teemu Pukki and Amido Balde.
But Johansen expressed little doubt that he would adapt to what he feels will be a more physical challenge.
"I'm a confident person because you need to believe in yourself," he said. "Of course it's a different type of football. Some of the away games are maybe harder than they are in Norway. But I will adapt to that. I have no worries about that, I just need to keep working hard."
Johansen, who is Lennon's first signing of the transfer window, aims to excite the Celtic support.
"I like the ball when it's on the ground," he said. "I'm a passing and creating midfielder. It's okay being a passing player but you cannot just stand and pass the ball. You need to create also. I hope to score goals, free-kicks, assists."
The Parkhead faithful might have to wait until after the visit of Motherwell on Saturday to see their new player in action though.
"My last game was on November 15 but I took the fitness test today and it went well," he said. "But matches are different than training, so we will see, we will be patient.
"I hope to play this weekend but I don't think it's going to happen. Maybe the next week."