Louis van Gaal says Marouane Fellaini is undroppable on current form.

Many tipped Fellaini to be one of the first players to leave Old Trafford when Van Gaal took over as Manchester United manager last summer.

After missing United's tour of the United States, Fellaini was jeered on his only pre-season outing for the club, in a friendly against Valencia at Old Trafford.

Fellaini did not start a Barclays Premier League game until the end of October but he has played a big role in United's success recently.

The 27-year-old has proved to be the perfect foil for Wayne Rooney in the last four matches, operating just behind the United captain in the number 10 role.

SEE MORE — Louis Van Gaal is bringing the best out of Fellaini

He has scored four goals in his last four games for club and country and Van Gaal has been pleased with the Belgian's efforts since day one.

"From the first training session he did what I asked," Van Gaal said.

"He was open and he wants to perform, so I am not surprised.

"He had an unlucky season (last year) because he was injured a lot of times and ill a lot of times and because of that he didn't play so much but when he was fit he has always played for me, more or less.

"I was looking for balance in the team and he can give a lot of balance in the team.

"I can change him also. It is dependable of the qualities of the opponent, but when he plays like he is playing now I cannot change him."

With Robin van Persie still out due to an ankle injury and Radamel Falcao out of favor, Fellaini is expected to line up for United in Saturday's home game against Aston Villa.

If United beat Villa and Arsenal fail to beat Liverpool, the Red Devils will move up to second ahead of Manchester City, who play Crystal Palace on Monday.

Being so high in the table would have been unthinkable during the early stages of Van Gaal's reign, but he is good spirits as United head into the home straight.

"I have a good feeling that we can continue against Aston Villa," he said.

"I said when we had 13 points from 11 games and we were getting a lot of criticism that we would see at the end of the season.

"It is still a rat race. Also Tottenham and Liverpool are still in it.

"We have given them a blow but we have to play against the first three still. A lot can still happen."

Van Gaal is not even ruling out an 11th hour tilt at the title.

When asked if his team could overtake leaders Chelsea, who lead United by eight points, Van Gaal said: "Mathematically, we can still do it."

It was expected Van Persie would return this weekend after the international break, but Van Gaal said the Holland striker has still not fully recovered from the ankle injury he suffered against Swansea on February 21.

"Robin van Persie is still injured," the United manager said.

"We have a process. He has to go to the final football coach before he comes into my group and he is not there yet.

"He is still not in my group."

Chris Smalling came off in the first half of England's 1-1 draw in Italy through illness on Tuesday and he is a major doubt for the Villa game.

"Smalling is ill so I don't know if he is available," Van Gaal said.

"(On Thursday) he was at the club, but in the medical department, doing his recovery and so on. (On Friday) I know already that he is not feeling well so it shall be difficult for him."

The most likely replacement for Smalling is Marcos Rojo, although he and Angel di Maria only returned to England on Thursday after their exploits with Argentina against Ecuador and El Salvador.

There is better news regarding Luke Shaw, though.

The left-back missed England's games against Lithuania and Italy due to a hamstring problem but is back to full fitness, according to Van Gaal.

The Dutchman said: "Luke Shaw is in my group."