Romelu Lukaku is well on his way to justifying the £75 million Manchester United spent to sign him from Everton this summer.

The Belgian has been hugely impressive in his first two Premier League games for the club, scoring two goals against West Ham and another at Swansea City on Saturday.

United fans were interested to see whether Lukaku can fill the boots of Zlatan Ibrahimovic and, as it stands, he absolutely can.

So imagine how good the Red Devils' attack will be with both players to choose from.

Ibrahimovic has spent the summer recovering from a nasty knee injury suffered against Anderlecht in April, which saw United decide against renewing his contract.

However, in typical Zlatan fashion, the 35-year-old striker has stunned doctors with a miraculous recovery.

There are now rumours of Jose Mourinho offering Ibrahimovic a new short-term deal, which ESPN's Andy Mitten reinforced on Sunday.

According to Mitten, Ibrahimovic could sign a new contract as early as next week given how ahead of schedule he is.

The question United need to ask is whether the Swede is actually ready to return, because the initial diagnosis said he would be out until the new year.

Well, Ibrahimovic now appears to have answered that question with a pretty incredible Instagram post.

In the video below, captioned "Which knee?", Ibra powerfully kicks a punchbag not once, but twice with the leg he injured back in April. Check it out.

The man is made of steel. It's only been four months since Ibrahimovic damaged his right knee, yet he's already able to acrobatically kick punchbags.

Should he sign a new deal at United this week as expected, one issue to address will be what number to wear.

Lukaku, with his permission, has inherited the No.9 jersey, as the Belgium international explained earlier this summer.

"I used to play with the 10 because my mother's birthday is on October 10, so it's the 10th month of the year," Lukaku said.

"I asked for the number nine because I'm a striker. Strikers play with No.9. It's a nice number, and I asked the permission of Zlatan Ibrahimovic."

Ibrahimovic will have to settle for a different number, then, but he will have no complaints if it ends up being No.10.

Now that Wayne Rooney is at Everton, the famous No.10 jersey is available, which Ibrahimovic wore at Paris Saint-Germain before joining United.