London: Celtic manager Neil Lennon says his squad needs freshened up in the January transfer market after his side put in a "flat" performance in a 1-0 home win over Partick Thistle on Wednesday.
The Hoops secured their eighth consecutive win in the Scottish Premiership to maintain their 11-point lead at the top of the table.
It was the third consecutive 1-0 win for Celtic, who have now gone 19 games unbeaten in the league and haven`t conceded in their past seven domestic matches.
However, the Hoops manager said he expected better performances from his side, who will now face St Mirren on Sunday before taking a two-week winter break from domestic duties.
"We were flat, there is no question of that. We looked tired and we lacked a spark particularly in the final third," said Lennon, whose team have also won at St Johnstone and Inverness Caledonian Thistle over the festive period.
"There were some good bits of play but I, and the supporters, expect better.
"We had a poor second half in Perth and Inverness and today there has been a flatness. It looks like things are catching up with some of the players. We need this break and we are very heavy legged and they are mentally tired.
"There is no question that the squad needs freshening up with an injection of new blood.
"We will endeavour to do that as it`s starting to show a wee bit in our play.
"We will get better - there`s no question about that. We`re just going through a very tough period of games at the minute. Mentally it has taken its toll as well as physically.
"I think we are in a decent position financially where we can look to bring players in.
"I think the squad is thin and if we pick up a couple of injuries we look light for us. In terms of comparisons to other teams in the league we are still very strong but in terms of where I want to take the team and moving the club forward I think we need another injection of quality and that takes a bit of money.
"I am determined to bring players in to make the squad better in the latter half of the season to give some of the players, who have been magnificent for us this season, a hand."
Joe Ledley scored the only goal of the game in the Glasgow derby against Partick Thistle in the 39th minute for his fourth goal of the season.
The Welsh midfielder is out of contract in the summer and has been linked with a move away from Celtic Park.
However, Lennon said he was hopeful Ledley would sign a new deal with the Scottish champions.
"I`ve spoken to Joe over a number of weeks but it`s certainly not affected his performances. I thought he was our best player today by a considerable margin," the Celtic manager said.
"I want Joe to stay and he has shown great mental strength as it must be a very unsettling period for him.
"He has intimated that he would like to stay and we are hoping that we can speak to his representatives this week and get that finalised.
"He has been an important player for me and the club and he gives us a stability that we need.
"I can`t have all the players leaving for big money or bringing players in to develop for a couple of years. I need a spine of players to stay together - the likes of Scott Brown, Ledley and a few others like Kris Commons and Georgios Samaras - as they have been big players for us."