"None of these things are ever blank checks, that goes with any situation in any kind of race," Ryan said in a radio interview with WTAQ's Jerry Bader in his Wisconsin district.
Ryan added his reason for backing Trump is that "he won the delegates, he won the thing fair and square it's just that simple."
The speaker also shrugged off Trump saying earlier this week he wasn't "there yet" on endorsing Ryan in his upcoming primary next Tuesday.
"The only endorsements I want are those of my own employers in the first congressional district, that's really what my focus is," Ryan said.
Trump incurred widespread criticism after engaging in a public feud with Khizr Khan, the Muslim-American father who spoke out against Trump's proposed ban on Muslims entering the US at the Democratic National Convention.
The episode made Republicans recoil and beg Trump to return to attacking his opponent, Hillary Clinton, instead.
"He's had a pretty strange run since the convention. You would think you ought to be focusing on Hillary Clinton and all of her deficiencies," Ryan said. "She is such a weak candidate that one would think we would be on offense against Hillary Clinton and it is distressing that that's not what we are talking about these days."
Ryan repeated what has become his standard caveat on his support for Trump after the GOP nominee makes controversial statement as well: "If I see a situation where our conservative principles are being distorted then I'm going to stand up for those conservative principles. If I see and hear things that I think are wrong I'm not going to sit by and say nothing, because I have a duty to defend principles and our party's brand if I think they are being distorted."
Asked about Paul Nehlen, his primary opponent, who is telling voters that the speaker is aligned with Clinton, Ryan didn't mention him by name, but said he is "making stuff up to try and make it stick."
He portrayed his challenger as a carpetbagger, saying about his challenge, "it's an out of state insurgent campaign powered by these scam PACs, and with a lot of out of state people."
He said confidently about his prospects on Tuesday, "I feel very good where I am."