But he has agreed to extend his stay at Celtic Park beyond the end of the season.
"I'm very pleased to agree this new contract with the club," the right-back told the club's website. "I have really enjoyed my time so far at Celtic and have been fortunate to make a number of appearances already in the first team.
"This is now something I want to build on and I'm committed to doing all I can to work hard and ensure that I can feature more and more."
Caddis has made 15 appearances for Celtic but he has yet to start a Scottish Premier League game for the club.
The Ayrshire-born defender spent the second half of last season on loan at Dundee United, making 11 appearances for Craig Levein's team, many of them in midfield.
But he has only started one game this season, the Co-operative Insurance Cup win over Falkirk in September.
The 21-year-old has come off the bench three times under Mowbray, the last time in the Old Firm derby defeat at Ibrox on October 4.
And he spoke frankly about his frustration over his lack of opportunities while on international duty with the Under-21s last month.
Caddis said then: "I haven't really been given any sort of encouragement from the gaffer that the situation might change."
However, Mowbray has pledged to give Caddis the platform to make his name in the game.
The Celtic manager told the club's official website: "Paul is a young player who has great ability and great character.
"He is someone who I know has all that is required to have a very good future in the game and and we look forward to working with him to ensure that we give him every opportunity to achieve his potential."