Arsenal manager Arsene Wenger has welcomed the return of England midfielder Jack Wilshere from three months out with an ankle injury, but warned the "balance of the team" must always come first.
The 23-year-old has not played since needing an operation after hobbling off in the defeat to Manchester United at the Emirates Stadium on November 22.
Wilshere, though, has come through his rehabilitation quicker than expected, and is expected to be involved again at Crystal Palace on Saturday afternoon.
Wenger has praised the way the player has dedicated himself to a speedy recovery, during which he made some unwanted headlines off the pitch after being photographed holding a shisha pipe at a nightclub.
It was not so long ago the dynamic midfielder would have been a certain starter in the Arsenal XI.
However, with the likes of Santi Cazorla, Mesut Ozil and Alexis Sanchez all in impressive form as Francis Coquelin shields the defence, Wenger accepts there can be no guarantees of selection for anyone.
"Jack is a bit ahead of schedule and has worked hard with no big problems, so it's good to have him back," said Wenger.
"It is always difficult to come back straightaway. What is good is that [he is] already back (earlier than expected).
"That injury was on the left ankle. He had all his problems on the right ankle.
"It is a straightforward injury - once it's healed, there's no problem."
Wenger, though, added: "No matter who plays, you always worry first about the balance of the team, yes."
The Arsenal manager hopes Wilshere can put the negative headlines behind him.
"I don't know how everybody is but I think every professional footballer has to control his life and dedicate it to the game," Wenger said.
Arsenal can expect a stern test of their top-four credentials at Selhurst Park against a side which is now well organised and hard to break down under new manager Alan Pardew.
Wenger said: "They have found confidence again and they made positive results and that is what it is about when you are a manager.
"We always expect a passionate afternoon there."
Pardew has hailed midfielder Cazorla as Arsenal's stand-out player.
The 30-year-old Spaniard has been linked with a transfer to Atletico Madrid, but Wenger insists the diminutive midfielder remains very much integral to Arsenal's future plans.
"Until now he has been maybe the most consistent, since he has moved centrally his influence on the team has been bigger as well," Wenger said.
"He has extended his contract last year. I think he has still two years to go.
"You know our policy at the club, so I don't think there's anything special to worry about there.
"The suggestion (of a transfer bid) is only a suggestion. We have never been approached by anybody about him."
Wenger confirmed former Arsenal forward Thierry Henry had been back at the club this week working with the Academy as part of his first steps into a coaching career.
"It is good for our young players to be coached by him, a legend of the club," said Wenger.
Arsenal 2 Middlesbrough 0 player ratings
Arsenal 2 Middlesbrough 0 player ratings
1/22 Wojciech Szczesny
Back in the side, the Polish stopper had little to do other than save from Adomah. 6
2/22 Calum Chambers
Impressive distribution throughout, he was always looking to start moves down the right. 7
3/22 Gabriel Paulista
Communicated well on his debut despite the language barrier although he was booked for a cynical foul on Reach. 7
4/22 Laurent Koscielny
Marshalled the Arsenal backline without trouble. 7
5/22 Kieran Gibbs
His pace allowed him to play much of the game high upfield where he was a constant menace for the visitors. 8
6/22 Mathieu Flamini
Did his job effectively in midfield - and without getting booked. 6
7/22 Alexis Sanchez
His pace, power and skill was a constant thorn in Middlesbrough's side until he was rested late on. 8
8/22 Santi Cazorla
Dictated the whole game from midfield with an array of clever touches, passes and off the ball movement. 9
9/22 Mesut Ozil
The German's creativity created numerous Arsenal chances. 8
10/22 Danny Welbeck
Demonstrated strength and trickery in attack, but often rushed his efforts at goal. 7
11/22 Olivier Giroud
Took his quickfire goals brilliantly in another strong performance. 9
12/22 Tomas Mejias
Made a number of eye-catching saves in both halves. 7
13/22 Ryan Fredericks
On loan from Tottenham, the 22-year-old was given a tough time on his return to North London. 5
14/22 Kenneth Omeruo
The Chelsea loanee stood up to the Arsenal attackers early on, but faded after conceding. 5
15/22 Ben Gibson
The young defender was given a tough evening, but remained determined throughout. 6
16/22 Adam Clayton
Sometimes struggled to track the runs of Sanchez, but cleared what would have been his own-goal off the line. 5
17/22 George Friend
Caught out of position on occasions. 5
18/22 Patrick Bamford
The forward was penned back by constant Arsenal possession and was eventually subbed. 5
19/22 Grant Leadbitter
The set-pieces of the midfielder had little effect. 5
20/22 Lee Tomlin
The burly playmaker saw little of the ball and failed to make an impact. 4
21/22 Albert Adomah
The midfielder made a number of bursting runs into the Arsenal box and was Middlesbrough's most threatening player. 6
Ineffective in both boxes until his stoppage time header struck the post. 5
Asked if the French World Cup winner could one-day replace him as Arsenal manager, Wenger replied: "That would not be my problem, it would be a problem of the board to make that decision.
"Yes of course (he could be a future Arsenal manager). I have said that many times, but I have had many, many players who can do this job."
FA Cup holders Arsenal have been drawn away to Manchester United in the quarter-finals, with the tie to be broadcast on Monday March 9, kicking off at 7:45pm.
Wenger said: "It is certainly not the most prestigious timing for people who want to watch on television.
"Maybe it is more suited maybe for a Sunday game, but television has made that choice. We will adapt and have no problem with it.
"We just want to win, and play when we are told to play. What I want is to go to Wembley, no matter who we play."
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