Sir Alex Ferguson says Leicester City are capable of winning the Premier League but that their activity in the January market could be crucial.
Leicester returned to the top of the table at the weekend with a 3-0 win over Swansea City and currently sit two points clear of second-placed Arsenal, with Manchester City and Manchester United a further point behind.
They have been in fine form since April, when former boss Nigel Pearson ended a long stint at the foot of the division by winning seven of his last nine league games in charge, and former United boss Ferguson suggested they should now be considered serious contenders for the title.
"What is the manager, Claudio Ranieri, saying to the owners? Because if I were him I'd want an investment in January because this is a big opportunity," Ferguson said at the TechCrunch Disrupt London event.
"They could win the league the way they are playing at the moment and they have goals in their team. That is not the owners' problem. The problem for the owners is have they got the money? I think they have.
"Do they trust the coach? The problem will always lie with the coach because he has got to pick the team. Adding more players to it, he has only given himself a problem.
"At the moment, he can pick the same team because he has a limited squad and is doing very well, but if he wants to win the league, I think he should add to it, and I think there may be a great chance."
Ferguson first won the Premier League in the 1992-93 season, when Norwich City had led the table at the start of April but then lost 3-1 to United, who finished 10 points clear after winning their final seven games.
"When we won the league for the first time, Norwich led until the middle of March, the whole season, but we beat them at their own ground and won the league," he said.
"So, for a small club historically like Leicester City, they have a challenge. How far can they go with this present squad, can they last the whole season?"
The Premier League has not been won by a club other than United, Arsenal, Chelsea or Manchester City since Blackburn Rovers -- funded by wealthy owner Jack Walker -- finished a point clear of Ferguson's side in 1994-95.
"I was listening to Peter Schmeichel last week and what he was saying was fantastic, talking about how people are underestimating Leicester City," Ferguson continued, referring to the former United keeper, who is the father of Leicester No 1. Kasper.
"This is a team with fantastic vitality, speed, energy. Peter was saying at the moment Leicester are the best team in the league, without a doubt, but the question is: how long will it last? Have they the resources to continue throughout the season?"
Leicester's fine form has led to star players including Jamie Vardy and Riyad Mahrez being linked with top clubs.
Having led Aberdeen to unprecedented success in Europe in 1983, Ferguson acknowledges that upsetting the odds can bring drawbacks.
"When Aberdeen won the European Cup Winners' Cup, it was the greatest moment for Aberdeen in their history and it was the worst moment too, because five players left within a year," he said. "Gordon Strachan went to Manchester United, Mark McGhee went to Hamburg.
"Leicester may have a situation where some players love being at Leicester City and don't want to move and they will have some who do want to move to Manchester United, or they want to play for Liverpool or Real Madrid. It is natural, it is progress."