The Lions batsman and former captain has scored 170 first-team runs from seven innings this summer.
His highest total of 54 came when he opened the batting against Hook & Newnham Basics last month.
After an “honest conversation” between the pair, Park confirmed Miller (left) would open for the second team in the Hampshire League match against County Division 2 high fliers South Wilts at Bemerton
The decision means he will not feature in Saturday’s home Southern Premier League Division One clash with Old Tauntonians & Romsey (12.30pm).
Park explained: "We made the difficult call in that Martin Miller is stepping down to the second team.
“He had been doing well but he had one or two weeks off with family commitments and holidays.
“Within the squad, we have three opening batsmen. Last week, Martin batted at number four and, speaking to me, he just felt he wasn’t a number four or five in our side.
“We had an honest conversation and it was decided he would go into the second team to open the batting for this particular week.
“We have a squad of 15 or 16 and people really do need to keep performing within our team. We all need to keep contributing.
“George Wilson, who has also dropped out of the first team in the past couple of weeks, hasn’t stopped scoring runs.”
Miller is expected to be replaced by seamer Dan Conway, who is set to be available for the rest of the season after previously battling work commitments.
The Herefordshire Minor Counties pace bowler has taken eight wickets for Lions this summer – his best coming on the opening day of the campaign with four for 22 against Andover.
“Dan is back and he is not going to miss another game, which is brilliant news,” added Park.
“It’s nice to have him on board every week now. Hopefully, he can find a bit of form with the ball and strike early as a new-ball bowler.”
Promotion-hopefuls Bournemouth top the pile with eight wins from their opening 10 fixtures.
Old Tauntonians are just one place above the drop zone in eighth. They did, however, seal an impressive 16-run win over Hook & Newnham Basics last time out.
All-rounder Rob Newman struck an unbeaten 104 (having made 98* the previous week), while opening bowler Danny Mogg claimed four wickets.
Park said: “Looking ahead to the next few weeks, hopefully, availability is good, we can keep winning and take some momentum into August.
“Old Tauntonians & Romsey had a good win last week. They may have players back from university now and I think any team in this league can beat each other.
“My chat on Saturday will be that we need to respect the game and the opposition and try to play to the best of our ability as a side.”
Bournemouth: C Park, West, N Park, Webb, Denham, Woodruff, Hurley, Conway, Pack, Clutterbuck, Warner.
OTs & Romsey: Smith, Brown, K Trodd, R Newman, P Newman, Tognarelli, Bampton, Wathen, Vaughan, J Trodd, Dhariwal.