Rooney played in midfield during the weekend's FA Cup semi-final win over Everton.
The United skipper played in the middle of the park for United's 2-1 win over Everton in the FA Cup semi-final against on Saturday and he has played in a more withdrawn role on several occasions.
Smalling is quoted in the Manchester Evening News, saying: “Everyone knows he's got the football brain to do that.
“And the last couple of years he's had to fill in in that role and you can see he can do that role, because he's such a good footballer and so clever that no position fazes him.
“I think it adds another attacking player and a goalscorer, because Wayne Rooney's a goalscorer, and the more goalscorers we can get on the pitch is better for the team.”
Smalling is right about Rooney's football brain as he has always been a great reader of the game, but his passing ability, his ways of being creative in a deeper role as well as his goal-scoring capabilities demonstrate his versatility.
Given that Marcus Rashford and Anthony Martial have been in fine form of late, manager Louis van Gaal has a big job on to get those two players into the starting line-up along with the club captain - who seems to think that Rooney has a future as a midfielder.
It could also make United that bit more of an effective attacking unit, especially given the criticism that has been levelled at the side - and mostly the manager - for the team being a bit cagey and not expansive enough that they would sweep sides aside.