The talismanic striker tweaked a hamstring during Reading's 3-1 defeat at Peterborough United last week.
The injury prevented him from playing against Blackpool on Saturday so new Arsenal loan striker Benik Afobe was handed his debut in the 3-1 victory.
But Roberts' injury is not as bad as first thought and the Blackburn Rovers signing could return to the starting line-up for the crucial Upton Park six-pointer this weekend.
Royals boss Brian McDermott confirmed: "Jason could be back for Saturday, we'll have to wait and see.
"It's a slight hamstring. If he's right he could be back, but we don't know yet. It's not as bad as first feared which is great news."
Reading cemented second place in the Championship table thanks to Saturday's convincing victory over the Tangerines, and they opened up a four point gap over third-placed West Ham who drew 2-2 at Burnley.
It means they will stay above the Hammers even if Sam Allardyce's side win their game in hand at Peterborough United tonight.
If Roberts does pass a fitness test, Afobe is likely to drop to the bench having made his debut less than two days after arriving from Arsenal on loan for the rest of the season.
The 19-year-old impressed in Saturday's victory at the Madejski Stadium alongside Noel Hunt, but goals from defenders Ian Harte and Alex Pearce plus a third from midfielder Mikele Leigertwood sealed the points and made it nine wins from 11 matches for McDermott's in-form men.
And the Royals boss praised the attitude of fellow strikers Simon Church and Adam Le Fondre.
"The most pleasing thing was the response from Simon and Alfie," he stressed. "Justifiably, they would have thought they would start and I understand that, but my gut feeling was to put Benik in. He's got a really good pedigree and will be a good player.
"I spoke to Churchy and Alfie because they're really important to me. Their reaction was first class."
And he added: "I agonised over the decision, it was a big decision but their reaction sums up the group. They both want the team and the club to do well.
"I felt Benik was the right man and he did really well, I was delighted with the performance. They're all in it together."
Reading have sold out their 3,000 allocation for the trip to Upton Park and a reunion with ex-coach Wally Downes, now Allardyce's No.2.
McDermott's men defeated West Ham 3-0 at the Madejski Stadium in December and he declared: "I'm genuinely looking forward to it, a full house and it's what football is all about. They have a fantastic manager, Wally Downes is there too and we're looking forward to going there and trying to put on a performance.
"It's two teams up at the top end of the League, and 10 games ago we would have snapped your hand off to be where we are."
** READING have now sold all their 2,450 allocation for the trip to Brighton on April 10 **