But two Japanese internationals will play club rugby in Dunedin this season, including a hooker. One is expected to debut shortly.
Otago coach Tony Brown said Coltman has a bulging disc in his neck and he was waiting for more medical advice on how long he would be sidelined or if he could play at all this season.
Coltman suffered the injury in a tackle in a pre-season club game for Alhambra-Union.
A former New Zealand colt, he had impressed for Otago over the past couple of seasons and had been a member of the Highlanders wider training squad for the last two years.
Otago B hooker Sam Anderson-Heather has been playing in Germany and is expected back in Dunedin shortly, to play for the Dunedin club. He has been hampered by injury over the past couple of years, after breaking his leg.
Brown said two Japanese international players, hooker Shota Horie and halfback Fumiaki Tanaka, would play club rugby in Dunedin, both for Zingari-Richmond, and if they played to sufficient standard could play for Otago. Neither has signed a contract with Otago.
Horie has already arrived in Dunedin and may play for Zingari-Richmond in the next couple of games, although he is still waiting for a clearance.
Tanaka will arrive at the end of next month, after he gets married.
The Japanese club season finished at the end of March.
Other Japanese club players are playing in Dunedin but none of them has been signed by Otago.
Brown has spent the bulk of the past eight years playing and coaching in Japan.
Both Horie and Tanaka played for Panasonic Wild Knights, the team coached by Brown.
They played at the Rugby World Cup last year for Japan and are quality players.
Brown said he had spoken to Highlanders and All Black hooker Andrew Hore about his domestic rugby plans but nothing had been decided.
Hore had joined the Highlanders after playing more than 100 times for the Hurricanes and is back living in Otago. He is no longer contracted with Taranaki, where he had played on and off over the years.
Hore played 11 games for Otago, the last of those in 2000.
Wing Hosea Gear was reported to have signed with Otago but both Brown and union change manager Jeremy Curragh said that was not the case. Gear had also shifted south to the Highlanders but his domestic future is unknown.
With the union running on a tight budget, no money would be available to pay additional players.
If Gear and Hore are picked for the All Blacks for the internationals in the autumn, which is a distinct possibility, they would not be available for Otago.
