Arsenal cannot afford to let Theo Walcott leave the club, according to ex-Gunners defender Sol Campbell.
The 23-year-old England forward has yet to agree a new contract, with his current deal set to expire next summer.
"Theo is a big player," Campbell told BBC Sport. "You don't want to lose him for the best years of his football.
"For the next five years, I'd pay to keep him. He's a young lad, a good lad who scores goals, and you need to keep those types of players."
With Walcott entering the final six months of his deal and the transfer window about to open, Campbell added: "January is very critical. It is a critical moment because if you don't get it right in January you can just forget the rest of the season."
Following the departures of Cesc Fabregas, Samir Nasri and Robin van Persie in recent years, Walcott could become the latest high-profile exit.
"People love him, people hate him - but Theo is a good player, a great player, and he's growing every year," said Campbell.
"You can't lose him because his contract is running out or he wants a little bit more money. You've got to keep those type of players. We've lost too many over time.
"It used to be losing these players at 30 years old - now they're losing these players at mid-20s and that's crazy. You can't be losing players at mid-20s because of contract situations - it's crazy now."
Campbell made 211 appearances in two spells at Arsenal, winning two league titles and two FA Cups, and scoring in the 2006 Champions League final.
But his former club have not won a trophy since the 2005 FA Cup, were stunned by League Two Bradford City in the Capital One Cup this month and are 15 points behind Premier League leaders Manchester United.
Arsene Wenger's side returned to form with victory at Reading on Monday and are in the last 16 of the Champions League for a 13th consecutive season, but Campbell feels it is vital they bolster their squad in January.
"I think they should find some money somewhere and get some top players in and just go for it," said the 38-year-old.
"They have some top players, but I just don't think there's enough. Jack Wilshere epitomises what Arsenal are all about. He's got drive, a great football head, he wants to win. Arsenal need a few more like that."
The money available to Wenger for signings and salaries was restricted by Arsenal's move from Highbury to Emirates Stadium in 2006.
"Arsenal are not in a situation where they are going to go out of business," Campbell explained. "They can actually hedge their bets and go for it.
"It's about gambling at the right time and I think now it's a critical moment to gamble, to buy players, to invest in them.
"We can't keep on losing top players because you're never going to build anything. If top players are going to invest in you, you've got to invest in them. They won't take half [the money] to come to Arsenal. Arsenal are not at that level.
"They've got a wage structure they don't want to break. I think that's a big problem with attracting the real top players."
Arsenal's mixed start to the season has seen Wenger face intense criticism, but Campbell says the Frenchman should remain in charge.
"He is the right man for the job, but he has to realise that the playing landscape has changed and the market has changed," he added.
"You've got to sometimes take a risk. Taking a punt on a player 10 years ago for £500,000 might now be £7m. You can't always get these £500,000 players, turn them into great players and sell them for £20m.
"Seven years plus without a trophy for Arsenal is too long. Arsene would be the first to say that. Why not wait until January and just go for it?"