The 21-year-old forward joined the Sulphurites from Championship Middlesbrough on transfer deadline day, agreeing a loan move until January.
He was not registered in time to be able to play any part during Saturday’s 1-0 League Two defeat to Barrow, but was thrown straight in from the start as Town beat Nottingham Forest Under-21s 2-1 in the EFL Trophy on Tuesday evening.
Sivi was initially deployed out wide, but then moved into a more central role, lasting the full 90 minutes on what was just his second taste of senior football.
"I thought that he was great,” Weaver reflected. “He showed a lot of ability. He is going to be a handful for League Two defences.
"He is quick, he is aggressive on the front foot, he is unpredictable, so I think that he can make a good impact.
"He gave his all for the team. I love his desire to go and press and work hard, he is totally our type of player.
"I thought that he did well in both roles. He has got good legs and athleticism, so he can be direct as a winger but we wanted to have a look at him straight down the middle.
"He nearly scored and I thought he was excellent overall."
Sivi started his career at Leyton Orient, before signing a professional contract with Middlesbrough in May 2023. He scored five goals in 12 appearances for the Teessiders’ Under-21s during the 2022/23 season.