Rated as a potential rising star in the Premiership, the versatile back made five appearances for Carnegie having arrived for their Championship Cup campaign last month.
Umaga, 20, played three games at full-back but also featured at inside centre and fly-half.
Carnegie director of rugby Chris Stirling was impressed and explained: “He’s gone back to Wasps to now play some A League rugby but I’m hoping he’ll be back here.
“There’s a chance Jacob could return in time for our next Championship match at Doncaster Knights on December 29th and then stay for the rest of the season.
“It’s a deal that’s still in discussions; we’re in the process of talking to Wasps about it.”
It would be a major boost to Carnegie’s hopes of pulling away from the bottom of the Championship if they can retain the services of the Halifax-born player and son of former Rotherham Titans star Mike Umaga.
He scored a try on debut against Nottingham and kicked 50 points during his initial stint, Carnegie winning four of their five Cup games.
Stirling’s side have, then, already qualified for the quarter-finals – as have today’s in-form visitors Coventry – ahead of this afternoon’s final pool fixture.
Coventry inflicted Carnegie’s only competition defeat so far with a 51-32 victory last month and know if they can repeat that result they will usurp their rivals from the top of the pool.
Whoever finishes first will be guaranteed a home quarter-final.
Myles Thoroughgood, who has made just one appearance since arriving from New Zealand in October, replaces Umaga at No15.
Will Britton and Sam Nixon have also returned to Bath Rugby while Harry Davey replaces Chris Elder on the wing.
Up front, Matt Smith returns from injury, Andy Foster comes in for Jake Ilnicki, who is on the bench, Josh Bainbridge starts instead of Cian Romaine and Tom Hill joins the replacements.