City boss will wait on Silva
Derby will give Gareth Roberts and Craig Bryson as much time as possible to prove their fitness for Saturday's Championship clash with Leeds at Pride Park.
Left-back Roberts (calf) and midfielder Bryson (knee) both missed the 4-1 defeat at Leicester last weekend with injuries sustained during the 1-1 home draw with Cardiff.
They remains doubts for Saturday's match but manager Nigel Clough is hopeful that at least one of them will win the race to be fit.
"They're coming on slowly and they're 50/50 at the moment with regards to being available to face Leeds," said Clough. "We'll take them right to the wire, Saturday morning if necessary, to see if we can get one of them back at least.
"However, if either of them was to be involved it would have to be without risking their fitness. As much as we want them back and out on the pitch, we can't risk them because if they have a setback they could end up missing our entire Christmas programme which would entail something like six matches.
"It's something we're aware of and will take into consideration, of course."
Jamie Ward has missed the last dozen games with a troublesome hamstring injury and the diminutive forward will miss out again this weekend.
Derby have an impressive recent record against Leeds. The Rams are unbeaten in eight matches in all competitions against the Yorkshire side, winning the last seven on the bounce.
Leeds striker El-Hadji Diouf missed last week's derby win at Huddersfield due to a slight groin strain, but returned to training this week and is likely to feature.
Ross McCormack made his first start since returning from a long-term ankle injury to partner Luciano Becchio at Huddersfield and manager Neil Warnock may be tempted to stick with a winning formula.
Another forward, Luke Varney, will return from his three-match ban following his dismissal at Millwall, while centre-half Jason Pearce and midfielder Michael Brown have both had to patient following their respective suspensions by making do with a place on the substitutes' bench.
Warnock has no new injury or suspension problems and must decide whether to retain Jerome Thomas, on loan from West Brom, or hand a start to fellow winger Ryan Hall, who made an impact when introduced off the bench last week.
Leeds are chasing a fourth straight league win in their bid to close the gap between themselves and the top six.
Although Mancini has ruled Aleksandar Kolarov out of the Etihad Stadium encounter, Silva, who missed the Champions League defeat to Borussia Dortmund in midweek with a hamstring injury, remains in contention.
"We will try with David," said Mancini.
Gael Clichy and James Milner are both battling to recover from ankle and hamstring problems respectively, although Mancini is wary of pushing both men into action too quickly.
"It is a big risk because afterwards we have a lot of games between now and the end of December and we need all the players to recover."
With United boasting a three-point advantage but City having a better goal difference the two sides are in exactly the same position as they were ahead of the corresponding fixture last season.
On that occasion, City famously won through Vincent Kompany's header to seize control of the title race with just two games remaining.
There is far more football to play this time around but Mancini acknowledges the importance of the occasion.
"They can lose because they have three points more," said the City chief. "We have three points less and we can't lose."
Yet, despite his side's status as champions and the fact they completed a Premier League double over United last term, including that amazing 6-1 win at Old Trafford, Mancini insists the Red Devils are the favourites.
"They are better than us at this moment," said Mancini.
"We have only been here for two years. They are used to playing these games in the title race for 20 years. They have won everything for 15 years.
"You can't change this in two or three years. You need more time.
"For this reason they have a small advantage."