Robertson was at Celtic as a youth player, but the 23-year-old left-back was let go when he was 15 years old and he moved to Queen's Park.
The Scotland international defender moved to Dundee United in 2013 and switched to Hull City in 2014.
The youngster made huge progress during his time at Hull and joined Liverpool in the summer of 2017 for a transfer fee reported by Sky Sports to be worth £10 million.
McNamara was the manager of Dundee United from 2013 until 2015, and the former Celtic and Wolverhampton Wanderers defender has revealed that then Everton manager Roberto Martinez came to look at Robertson.
"I don't think we realised how quickly he would adapt,” McNamara told Sky Sports about Robertson. "Within a few months a number of clubs were watching him. Roberto Martinez at Everton came up to see him around Christmas. A few others enquired.”
Robertson is a very good left-back, and given that he is still only 23, the Scotland international has time to further improve and develop himself.
Working under a manager like Jurgen Klopp at Liverpool is only going to help the youngster in the coming years.