Conservative MP Tobias Ellwood warned that Vladimir Putin will take “full advantage” of a weakened West and is in the strongest possible position to do so.
Russia has denied it is planning an invasion, but has moved 100,000 troops near to the border with Ukraine.
It would not be the first time Ukrainian territory was seized, following the annexation of Crimea in 2014. NATO has warned there is a “real risk” of fresh conflict in Europe.
“Putin is taking full advantage of a weakened West,” Mr Ellwood told BBC Radio 4 Today on Saturday.
"We are looking risk-averse, somewhat timid.
“Putin’s ultimatum demanding NATOo push back, of course that was dismissed but that’s given him the pretext to say that there is an aggressor and that he must act.
“We see these combat-ready troop formations. He has actually boxed himself into a corner because so much effort has been put into this.
“He also recognises that he will never again be as strong as this to take advantage of the West’s weakness. I suspect that an invasion is now imminent.”
Chair of the UK Parliament Foreign Affairs Committee said the UK should be prepared to support Ukraine financially in the event of an invasion.
Tom Tugendhat told BBC Breakfast: “I’d like to see all of us going further, because one of the things that’s delaying the ability of the Ukrainian people to mobilise their armed forces to meet any such invasion is that has a huge effect on any country’s economy.
“If you take hundreds of thousands of people out of the workforce in order to stand guard they will have a real impact on jobs and lives in other sectors.
“We saw that over lockdown over the last couple of years – the impact that has. So, we need to be ready to support the Ukrainian people financially as well, and that may be with loan guarantees and things like that.”