Renshaw, who was signed as Cameron Bancroft's replacement for the club, is currently the side's top run-scorer. He made 513 in six four-day matches, including three centuries, and 180 runs in six One-Day Cup games. Notably, Renshaw's 1180 runs in 24 innings is the best by anyone in first-class cricket this year and narrowly so. He is five runs clear of Sri Lanka's Roshen Silva, who will likely take the top spot once the day-night Test in Barbados begins on Saturday.
"Matt sustained a fracture on the top of his finger," Somerset coach Jason Kerr said. "After speaking with Cricket Australia it has been agreed that he will return to Australia sooner rather than later.
"Sadly for us that means it is the end of his time with Somerset this season. It's a huge blow to us because he has been brilliant both on and off the field. He fitted into the dressing room very well and a player of that calibre is going to be missed."
Renshaw was expected to be available until the end of June, and return to the club in mid-August. His sublime form had helped Somerset get to the top the Division One table - taking them within reach of a maiden title win - prior to their innings defeat against Surrey on Friday. His century on first-class debut for the club also made him the 14th man to do so in Somerset's history and the first since Alviro Petersen in 2013.