Dorus De Vries
McManus, who is 35 years of age, had a short spell at Scottish club Dunfermline during which time he worked with De Vries.
The former Hibernian and Falkirk forward was impressed with the 35-year-old goalkeeper, and has revealed what he thought of him then.
Dorus De Vries
“I didn’t know an awful lot about Dorus when I first signed for Dunfermline,” McManus told The Scottish Sun. “But I remember the manager Stephen Kenny telling me to watch him in training.
“We played a small-sided game and my first thought was ‘How good is this guy?’. He was as good as anyone. He could have played another position if he’d wanted to.
“He can put a ball on your feet from 60 yards away. He can step up and play as a sweeper keeper, which is huge for a team like Celtic."
Dorus de Vries
Celtic recently signed De Vries from Championship club Nottingham Forest.
As announced on Celtic’s official website at the weekend, the Scottish Premiership giants secured the services of the goalkeeper on a two-year contract.
The Dutchman is an experienced goalkeeper who had been on the books of Forest since the summer of 2013.
During the 2015-16 campaign, De Vries kept 11 clean sheets in 43 Championship matches for Forest.
Back in 2014-15, the goalkeeper made just four Championship appearances for the Reds. During the 2013-14 campaign, the Dutchman kept one clean sheet in three league matches for Forest.
De Vries is expected to give Celtic goalkeeper Craig Gordon competition for a place in the starting lineup.