Davies has seen just 40 minutes of action since early November and has missed the last six internationals with a pectoral injury he picked up in the opening Dove Men Series Test with South Africa.
The British & Irish Lions Test star had returned from the summer tour of Hong Kong and Australia as one of the continent's form players but his season was disrupted when he attempted to tackle Springbok skipper Jean de Villiers early in the first half of Wales' 24-15 defeat in Cardiff.
Davies sat out the autumn games against Argentina, Tonga and Australia as a result and has also watched on enviously as Wales faced Italy, Ireland and France in the first three rounds of the 6 Nations. He briefly returned to the Scarlets side for their LV= Cup clash at London Irish earlier this month but his since continued his recovery away from a game environment.
"Jon's contributed really well in training this week. It's good to have him around, he adds quality into the playing squad but he's also a very experienced player in terms of what he's done in the game," said Scarlets head coach Simon Easterby.
"He worked really hard to get himself fit to potentially make the start of the 6 Nations tournament. Following medical advice we were happy to play him against London Irish and, despite coming through that initial 40 minutes of rugby, it's good that he took a break and didn't try to keep on going. Jon accepted that you've got to get it right before coming back and he's in a better place now."
A strong showing from Davies would give Gatland and co plenty to think about prior to the trip to Twickenham a week on Sunday.
Wing George North impressed on his move to the outside centre channel against the French last Friday and Ashley Beck scored a fine solo try for the Ospreys against Munster two days later but the availability of the Lions' starting No13 would be a huge boost ahead of journey across the Severn Bridge.
"I think Jon has a fighting chance of playing against England," said Wales defence coach Shaun Edwards.
"His fitness is excellent and he has been working incredibly hard with the conditioners. He just needs to work on his match fitness a bit and gaining some confidence. It is that type of injury where he can have the confidence to put his shoulder into a tackle.
"He is one of the best centres in the northern hemisphere and he has a left-foot kicking game, which certainly helps your cause. I thought George did very well in that position and Jonathan knows he will have to fight his way back into the team."