Vainikolo will be looking to make his mark ahead of the Galway-based Irish provinces' debut in the Heineken Cup against Harlequins in the opening round of Pool 6 matches on Friday, 11 November.
Pool 6 will also see Connacht face four times champions Toulouse and Gloucester, offering the prospect of a battle between the two explosive Vainikolos - Gloucester's England international Lesely and Connacht's new boy Fetu'u.
"Playing for my home country was a huge honour and being part of the World Cup was an amazing experience," said Vainikolo, who played for. Northland, Otago and the Super 15 outfit the Highlanders before coming to Europe.
"For some players it's a once in a lifetime achievement, so I'm delighted to have had the opportunity to test myself at the highest level. Being back in the Connacht squad is great.
"The weather isn't quite the same, but it's good to be back involved with the team and I'm now looking forward to getting stuck into the league and Heineken Cup."
Samoan international back row forward Ray Ofisa could make his 100th appearance for Connachtin the Round 3 clash with Gloucester, while coach Eric Elwood looks set to have the experienced duo of George Naoupu and Miah Nikora fully fit by the time his side makes their Heineken debut at The Twickenham Stoop.
The game against Harlequins will be Connacht's 100th European match, although the first 99 came in the Amlin Challenge Cup.