Celtic manager Brendan Rodgers admitted he needs to add more quality to his side after they had to come from behind to claim a 2-1 win over Partick Thistle on Tuesday.
The Hoops, who have already won the League Cup, are looking to retain the historic treble they claimed last season while making an impact in the Europa League with a tie against Zenit Saint Petersburg to come in February.
However, the Scottish champions have been quiet in this transfer window with Marvin Compper and Lewis Morgan the only new arrivals at Celtic Park.
Injury will deny the Hoops of German cap Compper's services for another month while Morgan has been loaned back to St Mirren until the end of the season.
And Rodgers, who claimed his 50th Scottish Premiership victory over Thistle, said he would be frustrated if the Glasgow giants can't get some more deals done before the transfer window closes at the end of January.
"I'd be very disappointed if we didn't. I think it's something that we need to do," the Celtic manager said.
"But the people behind the scenes are working very hard to get the types of player we want in.
"We could have had 20 players in here if we wanted to but we need quality. We need players who can make a difference, not just domestically.
"If we are going to do anything in European football we need extra quality in our squad.
"That doesn't come about that often so you've got really hard to find that and that's obviously why we need to take our time to ensure we get the right ones."
Celtic were made to work hard for the three points in the Glasgow derby as they returned to Scottish Premiership action following a three-week winter break.
The Hoops fell behind to a Connor Sammon penalty in the 34th minute before Scott Sinclair levelled with his own spot-kick 10 minutes after the break.
Substitute Leigh Griffiths then fired home a 70th minute winner to move Celtic 11 points clear of Aberdeen at the top of the table, with the Dons facing third-placed Rangers at Ibrox on Wednesday.
And Rodgers praised his players for their positive reaction to going behind.
"There were spells in the first half where we were good but we were our own downfall at times," the Northern Irishman said.
"We were loose sometimes in our build-up from behind so we gave them a couple of opportunities on counter-attack.
"We made changes in terms of the shape and dynamic of the team at half-time and I thought the boys were brilliant in the second half.
"We put more risk into the game taking off a defender and putting on an extra attacker but the players coped with it really well.
"It was a good test. There are not many times in our domestic football that we go behind.
"The problem is there is an expectancy that Celtic are going to win four or five nil every week, but that's not the case. Teams are well organised so you have to be patient.
"They had something to hang on to through their penalty but our reaction was very good and it really showed you the spirit and the quality of the team."