Youssouf Mulumbu says he has joined an “amazing” club after moving to Celtic.
The experienced former West Brom and Norwich midfielder, 31, was a free agent after leaving Kilmarnock at the end of last season.
The Scottish champions have also signed Leicester City defender Filip Benkovic, 21, on a season-long loan.
And manager Brendan Rodgers hopes to retain Moussa Dembele, 22, after Celtic rejected a “significant” bid for the striker.
He is also “highly unlikely” to feature against Rangers in Sunday’s Old Firm derby.
“We don’t want Moussa to go and I can’t see it happening,” Rodgers said on Thursday. “There’s not a huge list of players that can come in and offer the qualities Moussa gives us.”
Mulumbu’s only goal during his 20 games with Killie was in a 1-0 win against Celtic and the former Paris St-Germain player has made more than 300 club appearances.
After selling Stuart Armstrong to Southampton, Celtic missed out on his fellow Scotland midfielder John McGinn, who joined Aston Villa from Hibs.
Rodgers said on Thursday that the Scottish champions “were always on the lookout for a really aggressive number eight to play midfield”.
And Mulumbu told the Celtic website: “The first goal for me is to show to the manager that I’m ready.
“Anytime he needs me I will respond on the pitch. We need to do well in the Europa League, retain all the domestic trophies and continue winning the Glasgow derbies. It’s amazing to be part of that.”
Benkovic joined the Premier League side from Dinamo Zagreb earlier this month for a reported £13m.
He is now on his way north as Celtic bolster their options in the centre of defence.
“He’s a highly-rated young centre-half, big presence in both boxes, can play,” Rodgers said.
Meanwhile, Celtic have sent 18-year-old striker Jack Aitchison on loan to third-tier Dumbarton until January.
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