Those problems have lead the Scarlets to cut their contracts for next season. Scarlets Chief Executive Stuart Gallacher said: "We have taken the difficult decision to part company with both of these players at the end of the season," said Gallacher.
"The 26-week injury clause is standard within professional rugby contracts and is something that all players are aware of when they join us."
Thomas won the last of his 22 Wales caps in 2007 having joined the Scarlets in 2004 while lock Maling, who played 11 times for the All Blacks between 2001 and 2004, has spent less than a year at Llanelli since moving from Japan.
Gallacher said: "We will be in ongoing dialogue with them and will support them where possible in any future moves. We are grateful to Simon and Gavin for what they have done for the Scarlets."
Scarlets coach Nigel Davies said a similar issue regarding Dafydd James' contract is "ongoing", though the region is said to be close to announcing more "significant" signings.