Kris Commons left out of Celtic's Champions League squad
Gary Mackay-Steven, who is working his way back from ankle surgery, is named in the squad.
Simunovic looked to be on his way out of Celtic this week but a move to Italian side Torino broke down on transfer deadline day.
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Hide AdManager Brendan Rodgers said the Croatian defender would be welcomed back to the Parkhead club with “open arms” and has named him in his squad.
Celtic will face Barcelona, Manchester City and Borussia Monchengladbach in the group stage of the Champions League, kicking off with a match against Barca at the Nou Camp on 13 September.
Commons has not featured under Brendan Rodgers, while Ambrose played in the early European qualifiers but has since lost his place in the team.