It depends on what we mean when we say “medieval.” We’re talking about a period of a thousand years in which English changed quite a bit.

In the early period we’re talking about a variety of Old English languages Kentish, Mercian, Northumbrian, and West Saxon. None of these are really mutually intelligible to modern English. Take the Lords Prayer. Here’s a pretty standard English version from the NIV

Our Father in heaven, hallowed be your name, your kingdom come, your will be done, on earth as it is in heaven. Give us today our daily bread. And forgive us our debts, as we also have forgiven our debtors. And lead us not into temptation, but deliver us from the evil one.

Here’s an earlier form from Northumbrian Old English probably 7th century.

FADER USÆR ðu arðin heofnu Sie gehalgad NOMA ÐIN. Tocymeð RÍC ÐIN. Sie WILLO ÐIN suæ is in heofne and in eorðo. HLAF USERNE of'wistlic sel ús todæg, and f'gef us SCYLDA USRA, suæ uoe f'gefon SCYLDGUM USUM. And ne inlæd usih in costunge, ah is in heofne and in eorðo.

And here it is in Kentish Old English from the 10th century Exeter Book

fæder, þu þe on heofonum eardast, geweorðad wuldres dreame. Sy þinum weorcum halgad noma niþþa bearnum; þu eart nergend wera. Cyme þin rice wide, ond þin rædfæst willa aræred under rodores hrofe, eac þon on rumre foldan. Syle us to dæge domfæstne blæd,hlaf userne, helpend wera, 8 þone singalan, soðfæst meotod. Ne læt usic costunga cnyssan to swiðe, ac þu us freodom gief, folca waldend, from yfla gewham, a to widan feore

Now with the texts side by side some readers may be able to more or less parse out which sentence matches up with which. But on its own each language really isn’t intelligible to a reader of one vs the other. Even the various dialects of Old English aren’t entirely mutually intelligible.

After the Norman invasion and the mutation of the Old English dialects into Middle English dialects they become far more similar to modern English and begin to standardize a lot. Here’s the Wycliffe (1380) version of the passage

Oure fadir that art in heuenes, halewid be thi name; thi kyndoom come to; be thi wille don in erthe as in heuene: gyue to us this dai oure breed ouer othir substaunce; and forgyue to us oure dettis, as we forgyuen to oure gettouris; and lede us not in to temptacioun, but delyuere us fro yuel.

Most late medieval scholars should be able to jump from that to modern English. Just like most modern readers can work their way through Chaucer with effort. Pluck someone from the 6th - 11th century and they’d be leading a new language.