The Saints opted against sending on loan O'Brien-Whitmarsh this summer as he remains a prominent figure for the under-21s side.
The teenager took part in the senior warmups, alongside the substitutes, in order to gain a feel for the top level as Martin is eager to introduce him to the first team as soon as possible.
He spoke about the 19 year old and how it is important to establish a clear pathway into the first team.
“Unfortunately for Joe, he wasn’t involved. But for him to be around the team again, for where he has come from, is good.
“There was a lot of loan opportunities for Joe but he was injured last year and we felt it was best for him to stay in the building.
“He will develop with us and train with us. He’s done it a lot. He’s been really, really impressive. He is one of a long list of players in the academy who have huge potential.
“We have to make sure we have a clear pathway for him and a clear plan. At the minute, it involves him being around first-team training and performing really well for the under-21s.”
O'Brien-Whitmarsh left Ireland champions Cork City in January to join the club and has clearly caught the eye of Martin who will need a mix of young rotational talent for the upcoming cup games.