The Welshman said: "Jason and the Duke are fantastic players and when they are on top of their game there is no-one better in that division, but I also think David Graham has a very big future in the game hopefully with Wigan Athletic.
"Having played alongside all three in my time at the club, I know David is more than capable of scoring goals at that level.
"He proved it with Torquay United last season and if Jason or The Duke pick up an injury he will prove how good he can be for Wigan Athletic.
"I have a great deal of respect for all three of them and I hope between them they can score the goals that get Wigan into the Premiership because that is where the manager, the chairman, the fans, the players, everyone at the club deserves and wants to be."
The 26-year-old, who was squeezed out of first team contention by the red-hot form of Roberts and Ellington, made his Doncaster debut in their 2-0 defeat at Port Vale in Coca-Cola League Two.
He played the full 90 minutes in Staffordshire and was involved in some of his new club's best moves, but defeat dropped the South Yorkshire side down to 15th.
Roberts, who played 143 times for Latics scoring 22 goals, is expected to make his home debut for Doncaster when they take on Torquay United this weekend.
Roberts' old team-mate at the JJB Stadium, full-back Leighton Baines, travels to Azerbaijan today looking to make his third start for England Under-21s when they play their next European Championship qualifier on Tuesday night.
The 20-year-old, who played in his country's last two qualifying matches against Austria and Poland last month, was left on the bench at Ewood on Friday night when England beat Wales 2-0 thanks to goals from Newcastle's James Milner and Ipswich Town hitman Darren Bent.