MONACO — Although Lewis Hamilton and Mercedes management are not saying precisely what is holding up his new deal, others think they know.

Hamilton's contract runs out this year.

The defending F1 champion has been elusive about when he will sign the new one — reportedly worth a staggering 120 million pounds ($160 million) over three years — while head of motorsport Toto Wolff hasn't given a date either.

"I can only imagine that a delay can only involve money. And I should think it's such a grotesque amount of money that Toto's talking about, it probably is what's making his eyes water," Red Bull team principal Christian Horner said on Thursday.

"(Hamilton's) got an expensive lifestyle. He's a four-time world champion and I doubt he's cheap. I can only envisage that that's probably got something to do with the delay."

When asked about the contract on Wednesday, Hamilton was casual-sounding about not being rushed, saying "if it's not ready this week, and it's not ready the week after, (then) it's not ready."

Hamilton gives the impression he alone decides when to sign. Wolff says this is not so, yet gives no deadline.

"This is work in progress and we see no hurry to pressurize each other into signing a document that will eventually happen anyway," Wolff said. "It is in the process of just closing. There is a bit of email pingpong on details. I don't want to set a date because then you will be asking, 'Why hasn't it been done?'"

There is uncertainty surrounding the future of other F1 drivers, too.

Hamilton's Mercedes teammate, Valtteri Bottas, is fighting for a new deal next season, and Red Bull's Daniel Ricciardo is considering his options for 2019. McLaren is hoping two-time F1 champion Fernando Alonso stays, while Ferrari must decide whether to stick with Kimi Raikkonen. The veteran Finnish driver turns 39 in October, but has started the season well.

Hamilton has also spoken in the past of his fondness for Ferrari, prompting speculation he could drive alongside Vettel next season.

"I wouldn't mind," Vettel said when asked if he would like Hamilton for a teammate. He added: "I'm pretty sure that Lewis' priority lies with Mercedes. Everything else would be a big surprise."

Hamilton joked that a move to Ferrari "wouldn't happen" because Vettel has a veto on who joins.

Red Bull and McLaren, meanwhile, face uncertainty over their drivers.

As well as driving for McLaren this season, Alonso will race in the famed Le Mans 24 Hours endurance race in June. In January, he took part in the 24 Hours at Daytona. Last year, the 36-year-old Spaniard skipped Monaco to race in the Indianapolis 500, and plans to race in it again.

"It's usually around the summer time that things start really taking shape," McLaren executive director Zak Brown said. "Fernando will let us know what he wants to do pretty soon."

Ricciardo has been linked with Mercedes and Ferrari, with both teams offering him a more powerful car unless Red Bull improves.

"Daniel is fully aware that we (want) to make the best choices for the future regarding the power unit (engine)," Horner said. "He is very comfortable in the team. So once the engine scenario is sorted I think things will move reasonably quickly."

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Jerome Pugmire on Twitter: www.twitter.com/jeromepugmire