Grant and O'Connell have linked with the NEC club in Japan for a couple of weeks.
Otago coach Tony Brown said NEC needed a couple of players to help the club with training over the next two weeks.
He said it was good for the Otago players to go and experience training with a professional side.
Otago loose forward Lee Allan went on a similar trip early last year.
''They are not playing Super rugby and this is a professional setup and will be a good development tool for them,'' he said.
NEC is coached by former Highlanders coach Greg Cooper and was a top-six team in the Japanese professional league last year.
Former Highlander Cameron McIntyre played for them last year along with Tongan international Nili Latu and former Highlander and All Black Anthony Tuitavake.
The duo will play a couple of warm-up matches for the NEC side, with its proper competition not starting for about three months.
Grant captained Otago last year and trained with the Highlanders on and off at the start of the season as injury cover.
He made a couple of appearances off the bench in pre-season matches but was not in the squad when this season kicked off.
Grant (25) was primarily seen as a loose forward at this stage, but could play lock at a pinch, which he did a few times last year.
Brown is looking for a lock after promising youngster Jackson Hemopo was ruled out for the season because of turf toe.
He has undergone an operation and is expected to take six months to get back to full fitness.
The injury forced him out of the New Zealand Colts team that opens its campaign at the World Junior Championships in France tomorrow morning. Tom Franklin played most of last year but his regular locking colleague Rob Verbakel has moved to English outfit Northampton.
Brown said the likes of Blair Tweed, Josh Dickson and Michael McKee could come into consideration.
He confirmed no Otago players would be available to play in an invitation side that will play the Highlanders on June 21, a Friday night, at Forsyth Barr Stadium.
He had talked to players and club coaches and they all agreed club rugby the next day was more important. It was getting towards the business end of the club season and the priority was with the clubs, Brown said.
He had wanted the game to be played earlier in the week. The Highlanders, which are using the game as match practice, will play a team made up of Southland players.
