Downes was a doubt for Tuesday's EFL Cup clash with Stoke City, and ultimately missed out after failing a late fitness test, but the signs suggest that the central midfielder will be fine to feature this weekend.
Meanwhile, Fraser limped off late in the first half at St Mary's on Tuesday, just after returning from a one-match suspension following his dismissal against Leicester City.
Fraser will be fighting to be fit so he can face Everton, the club he has scored more goals against than any other in his career, having netted four against Toffees from his time with Bournemouth and Newcastle United.
Defender Yukinari Sugawara was also a doubt for the cup win over Stoke, but he was passed fit and started, like he is expected to do so again this weekend.
Martin picked a relatively strong team for that last 16 tie against the Potters, with Kyle Walker-Peters and Tyler Dibling the only two players who were given a proper rest from their regular starting XI.
Young winger Dibling was withdrawn at half time in the Saints' 1-0 defeat at Manchester City last weekend, but his manager confirmed that this was down to fatigue and not injury, so he is in line to return here.
In the rest of Southampton's injury concerns, goalkeeper Gavin Bazunu will be out for most of the season after undergoing surgery on his Achilles at the start of the season, so Aaron Ramsdale is set to continue as normal between the sticks, while a hamstring issue for Will Smallbone and a muscle problem for Ross Stewart will likely keep the duo out until after the November international break.
Southampton possible starting lineup:
Ramsdale; Sugawara, Harwood-Bellis, Bednarek, Manning, Walker-Peters; Dibling, Aribo, Downes, Mateus Fernandes; Archer