Vainikolo, who scored six tries for the Highlanders this season as a draft player from Northland, was one of 16 players named yesterday by the New Zealand Rugby Union to sign extended contracts.
Otago Rugby Football Union chief executive Richard Reid said the union had put an offer in front of Vainikolo and his agent to sign for the Otago union.
"We are aware Fetu'u is coming off his contract with Northland and we are talking to him and his agent," he said.
"We are actively trying to get him down here and have put something on the table for him to look at."
Reid said although he was never confident of signing any deal, he hoped to have something finalised in the next few days.
He declined to rate the chances of signing the Northland flier.
The Tongan-born 23-year-old scored two outstanding tries for Northland in its narrow loss to Otago last Friday night at Carisbrook.
Northland players have a bleak future with their side not invited, along with Tasman, to play in the Air New Zealand Cup next year.
The side is to play in the amateur Heartland Championship.
Reid said the union was also looking for other players, but declined to name them.
Reid had cut about $500,000 off last year's wage bill and, with captain Craig Newby moving overseas, there was some room to move within the salary cap.
He said Otago was not picking off one of Northland's best players, but was just doing business.
Vainikolo had a stand-out debut season after being picked out of the blue by Highlanders coach Glenn Moore.
He played in all 13 of the Highlanders games and was the side's leading try-scorer.
Just two seasons ago, Vainikolo was playing lower grade club rugby in Auckland before deciding to try his luck with the Cambridge Blues.
The NZRU announced yesterday Otago No 8 Steven Setephano had re-signed with the national union until 2011, while Otago hooker Jason MacDonald had signed until 2010.
Reid said both players were signed with Otago until the end of next year.
An offer had been made to All Black loose forward Adam Thomson and Reid hoped to meet the rangy player next week.
Other 2008 Highlanders who have re-signed with the national union until 2010 include Southland flanker Tim Boys, Southland hooker David Hall and Manawatu midfield back Johnny Leota.
The NZRU also announced Canterbury winger Sean Maitland and Auckland midfielder Benson Stanley had signed through to 2011.
Others to sign through to 2010 are Jacob Ellison, Serge Lilo (Wellington), Kurtis Haiu, Onosa'i Tololima-Auva'a (Auckland), Faifili Levave (Waikato), George Pisi (North Harbour), and Willie Ripia (Taranaki).
Auckland and former Highlanders prop Nick White has re-signed until the end of 2009.
NZRU general manager of professional rugby Neil Sorensen said with overseas offers an attractive lure for many players, the union did not underestimate how important it was to secure these players.
He praised the Super 14 franchises for creating a supportive environment for the players and the players still had a lot to offer the game in New Zealand.
