The forward joined third-placed Roma on loan in the transfer window seeking regular action to boost his chances of making Italy's World Cup squad after falling out of favour at Bayern Munich.
After making a promising start, Toni's plans were set back by a calf injury in January but he returned to training with his team mates this week and Italian media expect him to feature at some point as Roma bid to pull level with Milan in second place.
Chilean midfielder David Pizarro might return from a calf problem too, but skipper Francesco Totti will probably miss out again with the latest of a string of injuries.
Roma's midfield and attack may have been reinforced but coach Claudio Ranieri is likely to be more concerned about the defensive blackouts that have cost his side recently.
The Rome club let a two-goal advantage slip in the closing stages of last week's 2-2 draw at Napoli, days after conceding three goals in six minutes in a 3-2 home loss to Panathinaikos as they crashed out of the Europa League 6-4 on aggregate.
Those lapses could be why Ranieri has said several times that his side had no chance of catching Inter, who are seven points ahead of them.
Milan, who are four points behind the leaders, are less coy about their title ambitions.
"If we conquer three points against Roma we can really think about winning the championship," Brazil centre back Thiago Silva was quoted as saying by Thursday's La Gazzetta dello Sport.
A lot is riding on the next few days for Milan, who visit Manchester United in the return of their Champions League last 16 tie on Wednesday needing to reverse a 3-2 deficit.
In-form Brazilian forward Alexandre Pato looks certain to miss the Roma clash and has an outside chance of playing in Manchester.
His compatriot Mancini is expected to come in this weekend, with David Beckham favourite to fill in at Old Trafford against his old club.
Milan's Clarence Seedorf has fitness problems too and fellow midfielder Gennaro Gattuso is suspended this weekend.
Inter coach Jose Mourinho will have to watch Sunday's home game against Genoa from the stands as he serves the second part of a three-match touchline ban for a controversial handcuffs gesture made in a draw with Sampdoria two weeks ago.
Mourinho will be unable to call on suspended midfielder Esteban Cambiasso.
Juventus, who share fifth place with Napoli after last week's 2-0 defeat at fourth-placed Palermo, visit faltering Fiorentina on Saturday.
