The 23-year-old has been on trial with the Lions and bidding to impress after being let go by Fulham at the end of last season.
He has played in both pre-season games so far at Dartford and Saturday’s 2-2 draw at Stevenage, after which Den supremo Holloway revealed he needs to learn more about the left-back before deciding on whether to offer him a permanent deal.
Ollie said: “Briggs is growing on me.
“I need to find out one or two other bits about him. I go on relationship - and if people change those I don’t like it because I wouldn’t change a relationship.
“I know I’m in the right place to do that and I have to make sure he wants the same thing as I do and what has ever stopped him getting there I can help him with.
“If I bring someone to my football club who might not start well and can’t handle it, then I’m wasting my chairman’s money.”
The boss added: “I need to try out certain things.
“I can’t understand for the life of me why with his athleticism and wonderful left-foot that I've already seen Fulham dreamed of letting him go.
“At one time he was in the England set up and doing all these bits and pieces.
“He might be frustrated and doesn’t feel loved.
“I can’t deal with that if they don’t come fighting back.”
Holloway now intends to step up his assessment of the defender before deciding whether to pursue the deal any further.
The boss admitted: “I haven't watched him as much as I should have done.
“I like Scott Malone, so I have to make sure I bring in someone who can push him and challenge him.
“I need to sit down with him (Briggs) and watch some of his games.
“I think he just stands there in a game and thinks ‘how good am I doing?’
“You can’t let those thoughts in, I need to see if I can cure that.
“If I can’t then I won’t do anything. If I can then we could have one hell of a player on our hands.”
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